Edge: improve common capability determination
Edge: improve common capability determination

This improves the determination of common capabilities
such that two codecs will be considered equal even if
the number of channels does not match. In that case,
the lower number will be used.

See also https://github.com/w3c/ortc/issues/569#issuecomment-256213596

webrtc/adapter,jan-ivar/adapter,Acidburn0zzz/adapter,xdumaine/adapter,Acidburn0zzz/adapter,xdumaine/adapter,jan-ivar/adapter,Acidburn0zzz/adapter,webrtc/adapter