Proposal for WebIDL for bundle policy from JSEP

In JSEP, it says we need a "bundle policy".  See for example:
http://tools.ietf.org/html/draft-ietf-rtcweb-jsep-07.  But we're
lacking the WebIDL in the W3C spec.

I propose:

enum RTCBundlePolicy {
  "balanced",
  "max-compat",
  "max-bundle",
}


RTCConfiguration {
  // ... iceServers, etc
  RTCBundlePolicy bundlePolicy;
}



Comments welcome.  If there are no objections, I'll make a pull request.