DTLS media profile fix for Chrome / Firefox / Opera 

Chrome and Firefox incorrectly declare DTLS with a media profile of "RTP/SAVPF". 
RFC 5764 [1] states that it should be "UDP/TLS/RTP/SAVPF".

This is currently being used in a production environment and working well.
Based on hack presented here: https://groups.google.com/d/msg/sip_js/12mlRuOlEHg/_q_WIlnFBykJ