AUTO_SEGS_N not changed after #1103 fix, because
most of responses has large size and with this
value (8) we can cover higher percentage of
responses

Now we use cleanup field instead of `old_head`, cleanup also used
during http1 request adjusting.

Allowed to use unknown method for headers that stored in dynamic table.
Before if tempesta received such request it was dropped.

Unknown method is method that processed as _TFW_HTTP_METH_UNKNOWN.

`tfw_http_add_hdr_clen()` replaced by new function
`tfw_http_resp_term_add_hdr_clen()`. Now it constructs
content-length header into headers table, without
skb modification as it done before. The headers
copies to response in the tfw_http_adjust_resp() along
with other headers.

`tfw_http_msg_hdr_xfrm()` - deleted, because it's un-
used. Some of functions that were used only by
`tfw_http_msg_hdr_xfrm()/tfw_http_msg_hdr_xfrm_str()`
not deleted, because we consider them as library
functions. For instance: `tfw_strcpy_comp_ext()`.

`ss_skb_get_room()` could be lib function, but it's
just a wrapper for `ss_skb_get_room_w_frag()`.

`__hdr_is_singular()` was used during adding headers
configured by administrator, but we treat adding
singular RAW headers via `resp_hdr_add` as
misconfiguration, there is no sense to check it for
each header.

In this patch we optimize header skipping logic that
applies in header modification for HTTP1 request/re-
sponse and HTTP2 response including cache.

       Overview of current behavior.
It consists of two parts: skipping and addition.
During response transformation or copying we
skipping headers that must be substituted or deleted
using `tfw_http_hdr_skip()`, when all headers from
original response are copied we add new headers
(directive (resp/req)_hdr_(add/set)) and add headers
that must be substituted ((resp/req)_hdr_set).

What have done:
1. `tfw_hdr_mods_t::spec_hdrs` turned into bitmap.
2. `tfw_hdr_mods_t::spec_hdrs` contains used only
    for *_hdr_set directives, headers related to
    *_hdr_add must not be skipped, thus excluded from
    `spec_hdrs`.
2. `tfw_http_hdr_skip()` only iterates over *_hdr_set
    headers and doesn't check `append` flag.
3. added `tfw_hdr_mods_t::scan_off`, this is offset
   where we start itarating headers and comparing the
   name. It's the case when modification not found by
   special header index or hpack index.
4. changed the layout of `tfw_hdr_mods_t::hdrs`,
   now we storing headers in following way:

   .----------------------------------------.
   |          `tfw_hdr_mods_t::hdrs`        |
   :----------------------------------------:
   | Special headers *hdr_set               |
   :----------------------------------------:
   | Hpack indexed raw headers *hdr_set     |
   :----------------------------------------:
   | Non-indexed raw headers *hdr_set       |
   :----------------------------------------:
   | All headers *hdr_add                   |
   '----------------------------------------'

   due this structure we can iterate only over
   unindexed raw headers.

Note: Looks like iterating over headers modification
table especially for removing is more profit approach,
because if modification applied we will not iterate
over this opearation again, we using it during http2
request headers modification, but it has disadvantages.
For instance we must realloc header table or split
skipping and adition(similar with current approach) and
such approach can't be used with current cache
architecture.

Just fix to commit with logic unifying, this patch
adds abillity to adding headers to HTTP2 request,
without this header will be substituted even if
req_hdr_add directive was used.

Add a new method intended to close parsed HTTP1.1
method. `tfw_http_msg_hdr_close()` is not suitable
in this case, it has a lot of logic that unnecessary
for method.

fix 1:
Skip trailer headers during copying regular headers
to not duplicate them in headers and in trailer.

fix 2:
Call `mark_spec_hbh` for headers with only LF in the
end of a message.

fix 3:
Headers `connection` and `keep-alive` marked as
hop-by-hop during parsing, it's allowed to remove
following conditions:
```
if (hid == TFW_HTTP_HDR_KEEP_ALIVE
     || hid == TFW_HTTP_HDR_CONNECTION)
```
do only simple `if (tgt->flags & TFW_STR_HBH_HDR)`.

Before this patch `keep-alive` was marked as HBH, but
only if `keep-alive` specified in `connection` header.
RFC 9110 7.6.1 say that intermediaries SHOULD remove or
replace such headers even if the not listed in
Connection.

We had a bug during the suffix match in function
`tfw_http_search_cookie()`, before comparing
the name we store current chunk `t = *chunk`, then
modify and compare the chunk, after we rostore the
chunk `*chunk = t;` that leads to header corruption,
because macros `TFW_STR_EQ_CSTR` may assign new
address to `chunk`, therefore restoration happens to
a newly assigned adress instead of original adress in
`chunk`. Fixed by storing address to temporary
variable and then restore `data` and `len` by this
adress.

`__tfw_str_eq_cstr` rewritten to inline function.
Inline functions is more clear, less error prone and
suitable in this case, because we don't need to define
tmp vars and explicitly save values, only move `chunk`
pointer forward. Generated assembly will be the same.

We must copy a mark from old skb head to new, otherwise
we will lose the mark.

Call `mark_spec_hbh` only for parsed special header
and do not iterate over headers table.

Validating a syntax of the `Host` header, to catch
protocol violations.

 - return replaced with `goto clean`
   in `tfw_h1_adjust_req()`

Before this patch we compared the Host header and
uri's host as strings including port part. However, in
case when explicitly specified default port in one
of them, but not specified in the second we had error.

Example:
uri: tempesta-tech.com
host: tempesta-tech.com:80

In this case uri and host must be treated as the same,
due to 80 port is default and can be omitted.

In this patch we parse uri and host in the same way,
we mark host part from the uri and from Host header as
TFW_STR_VALUE excluding the port (e.g ":80") part.
Port we parse and save into `TfwHttpReq::uri_port`
for uri port and into `TfwHttpReq::host` for host
respectively. Then in `frang_http_host_check()` we
compare host parts that marked as TFW_STR_VALUE
(use ":" as stop symbol) and separately compare ports.

This commit adds special case for setting Host header
in the request using `req_hdr_set` directive. We
simply write the new Host header to the request
skipping the old one during request adjusting. However
we don't update original Host header in headers table,
to be able to use original header. We need original
header during caching response, in this case we
make the key using original Host header. We do so,
because we always find response in the cache using
original host header.

Add this overriding it exists in original version of
tfw_h1_adjust_req().

In case when request has absolute URI that looks like
this: `http://tempesta-tech.com` - without trailing
slash, `uri_path` will be empty, this commit handles
this case.

Userinfo subcomponent is depricated by RFC 9110 4.2.4

Empty host in URI prohibited by RFC 9110 4.2.1.
Example of URI with empty host: "http:///path"

Free cleanup structure in safe way, to prevent
use-after-free. We free clean structure immediately
after error to get free memory to create the response.

Write method string directly to access log instead of
using method id and table with static names. It gives
an abillity to write to log methods that not listed
in `tfw_http_meth_t`.

Separate HEAD to GET from PURGE to GET logic