Add reference for DTLS-SRTP Protection Profiles and update references…

… for the WebRTC DTLS ClientHello DoS (#2550)

* Add DTLS certificate / SDP fingerprint attribute verification to WebRTC chapter (53.2)

see #2098

* update references for ClientHello DoS

* add reference for dtls-srtp protection profiles

* fix markdown linter

5.0/en/0x53-V53-WebRTC.md:74:105 MD047/single-trailing-newline Files should end with a single newline character

5.0/en/0x53-V53-WebRTC.md

@@ -70,4 +70,5 @@ For more information, see also:
 * [RFC 8825 - Overview: Real-Time Protocols for Browser-Based Applications](https://www.rfc-editor.org/info/rfc8825)
 * [RFC 8826 - Security Considerations for WebRTC](https://www.rfc-editor.org/info/rfc8826)
 * [RFC 8827 - WebRTC Security Architecture](https://www.rfc-editor.org/info/rfc8827)
-* WebRTC DTLS ClientHello DoS: [A Novel DoS Vulnerability affecting WebRTC Media Servers, Enable Security](https://www.rtcsec.com/article/novel-dos-vulnerability-affecting-webrtc-media-servers/)
+* The WebRTC DTLS ClientHello DoS is best documented at [Enable Security's blog post aimed at security professionals](https://www.enablesecurity.com/blog/novel-dos-vulnerability-affecting-webrtc-media-servers/) and the associated [white paper aimed at WebRTC developers](https://www.enablesecurity.com/blog/webrtc-hello-race-conditions-paper/)
+* [DTLS-SRTP Protection Profiles](https://www.iana.org/assignments/srtp-protection/srtp-protection.xhtml)