Randomize the order of DTLS ClientHello extensions, to reduce potential ecosystem brittleness. This is a WebRTC specific follow-up to https://groups.google.com/a/chromium.org/g/blink-dev/c/bYZK81WxYBo/m/lKLrZ_P2BwAJ which launched successfully a while back. WebRTC uses DTLS (datagram TLS over UDP) multiplexed with STUN and RTP and also uses a SRTP specific extension (use_srtp defined in RFC 5764) to negotiate encryption keys. Middleboxes might expect the use_srtp flag in a certain position which changes with this feature.