add comment to prevent security scan false positives (#5973)

internal/protocols/webrtc/inbound_track.go

@@ -334,6 +334,9 @@ func (t *InboundTrack) start() {
 
 			pkts, err2 := rtcp.Unmarshal(buf[:n])
 			if err2 != nil {
+				// it's currently impossible for this to be triggered,
+				// because malformed RTCP packets are already blocked by pion/interceptor
+				// and in particular by the NACK interceptor.
 				panic(err2)
 			}