Fix janus-gateway: use unified plan with fallback

Fixes "panic: TypeError: offer SDP semantics does
not match configuration"

Author: tmatth

README.md

@@ -61,6 +61,7 @@ Check out the **[contributing wiki](https://github.com/pion/webrtc/wiki/Contribu
 * [Jadon Bennett](https://github.com/jsjb)
 * [Lukas Herman](https://github.com/lherman-cs) - *C Data Channels example*
 * [EricSong](https://github.com/xsephiroth) - *Implement GstV4l2Alsa example*
+* [Tristan Matthews](https://github.com/tmatth)
 
 ### License
 MIT License - see [LICENSE](LICENSE) for full text

janus-gateway/streaming/main.go

@@ -60,6 +60,7 @@ func main() {
 				URLs: []string{"stun:stun.l.google.com:19302"},
 			},
 		},
+		SDPSemantics: webrtc.SDPSemanticsUnifiedPlanWithFallback,
 	}
 
 	// Create a new RTCPeerConnection

janus-gateway/video-room/main.go

@@ -43,6 +43,7 @@ func main() {
 				URLs: []string{"stun:stun.l.google.com:19302"},
 			},
 		},
+		SDPSemantics: webrtc.SDPSemanticsUnifiedPlanWithFallback,
 	}
 
 	// Create a new RTCPeerConnection