Proposal for RTCRtcpMuxPolicy

At IETF 91, we decided to split the bundle policy an rtcp mux policy into
separate policies in JSEP (instead of having "max-bundle-and-rtcp-mux").

Meanwhile, I also created a pull request for RTCBundlePolicy, based on
previous discussion on the list: https://github.com/w3c/webrtc-pc/issues/137
 (the PR has balanced, max-bundle, and max-compat, but not
max-bundle-and-rtcp-mux).

So, now we need an RTCRtcpMuxPolicy.  I propose we make it just like
RTCBundlePolicy, which is, to add it to RTCConfiguration like so:


enum RTCRtcpMuxPolicy {
  "optional"  // RTCP candidates are gathered, but discarded if the remote
endpoint can mux RTCP.
  "required",  // RTCP candidates are not gathered
};

dictionary RTCConfiguration {
  // ... iceServers, bundlePolicy, etc
  DOMString rtcpMuxPolicy = "optional"; // see RTCBundlePolicy
};



Of course, we want this to match JSEP, so we may need to wait to see what
JSEP decides are the names for "optional" and "required".