When the -port configuration option is used, the default onion listening port will now
be derived to be that port + 1 instead of being set to a fixed value (8334 on mainnet).
This re-allows setups with multiple local nodes using different -port and not using -bind,
which would lead to a startup failure in v28.0 due to a port collision.
Note that a HiddenServicePort manually configured in torrc may need adjustment if used in
connection with the -port option.
For example, if you are using -port=5555 with a non-standard value and not using -bind=...=onion,
previously Bitcoin Core would listen for incoming Tor connections on 127.0.0.1:8334.
Now it would listen on 127.0.0.1:5556 (-port plus one). If you configured the hidden service manually
in torrc now you have to change it from HiddenServicePort 8333 127.0.0.1:8334 to HiddenServicePort 8333 127.0.0.1:5556, or configure bitcoind with -bind=127.0.0.1:8334=onion to get the previous behavior.
(#31223)