Ignore inactive media. (#1365)

* Ignore inactive media.

Seeing some errors of
"track info not published prior to track".
Happens when trying to configure publisher answer for audio
for DTX and stereo and trying to find a pending track.
There are cases where there are inactive m-lines in SDP
that is hitting this.

* fix sense

pkg/rtc/participant_sdp.go

@@ -191,6 +191,10 @@ func (p *ParticipantImpl) configurePublisherAnswer(answer webrtc.SessionDescript
 	for _, m := range parsed.MediaDescriptions {
 		switch m.MediaName.Media {
 		case "audio":
+			_, ok := m.Attribute(sdp.AttrKeyInactive)
+			if ok {
+				continue
+			}
 			mid, ok := m.Attribute(sdp.AttrKeyMID)
 			if !ok {
 				continue
@@ -198,6 +202,10 @@ func (p *ParticipantImpl) configurePublisherAnswer(answer webrtc.SessionDescript
 			// find track info from offer's stream id
 			var ti *livekit.TrackInfo
 			for _, om := range parsedOffer.MediaDescriptions {
+				_, ok := om.Attribute(sdp.AttrKeyInactive)
+				if ok {
+					continue
+				}
 				omid, ok := om.Attribute(sdp.AttrKeyMID)
 				if ok && omid == mid {
 					streamID, ok := lksdp.ExtractStreamID(om)