Use intersection of codecs to generate rtcp-fb

Update MediaEngine codec creation to take into account remote
and local rtcp-fb. Before we would incorrectly always take
the remote rtcp-fb and ignore local.

Resolves #2943
Resolves #2944
Resolves #1968

rtptransceiver.go

@@ -78,6 +78,7 @@ func (t *RTPTransceiver) getCodecs() []RTPCodecParameters {
 			if codec.PayloadType == 0 {
 				codec.PayloadType = c.PayloadType
 			}
+			codec.RTCPFeedback = rtcpFeedbackIntersection(codec.RTCPFeedback, c.RTCPFeedback)
 			filteredCodecs = append(filteredCodecs, codec)
 		}
 	}