Do WebRTC encoding/decoding types have the single-codec restrictions?

[markafoltz]

The spec is being updated to reject audio and video MIME types that do not specify a single codec.

We should determine if browsers follow this logic when the encoding and decoding type is webrtc, by updating WPTs, and then discussing the desired behavior.

If they do not, we will have to fork the algorithms for determining the validity of a MIME type further.