[H264][Simulcast] Implement the simulcast logic for h264 encoder

webrtc/video/payload_router.cc

Index: webrtc/video/payload_router.cc
diff --git a/webrtc/video/payload_router.cc b/webrtc/video/payload_router.cc
index 3be5882cdbf2172928fe312caf2a9b3401d1ea9b..d0f84f81a5c924ee672aed3a81aaf3e0ef2f5b4a 100644
--- a/webrtc/video/payload_router.cc
+++ b/webrtc/video/payload_router.cc
@@ -75,6 +75,7 @@ void CopyCodecSpecific(const CodecSpecificInfo* info, RTPVideoHeader* rtp) {
     }
     case kVideoCodecH264:
       rtp->codec = kRtpVideoH264;
+      rtp->simulcastIdx = info->codecSpecific.H264.simulcastIdx;
       return;
     case kVideoCodecGeneric:
       rtp->codec = kRtpVideoGeneric;