[rtp_rtcp] Fix potentional time difference between rtp and rtcp packets.

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
index 33e23ec01a634238e86ac3e78cfda5a9cdc51112..09be51811f57123a4d3164c52468da856d77850b 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -291,6 +291,7 @@ void ModuleRtpRtcpImpl::SetSequenceNumber(const uint16_t seq_num) {
 bool ModuleRtpRtcpImpl::SetRtpStateForSsrc(uint32_t ssrc,
                                            const RtpState& rtp_state) {
   if (rtp_sender_.SSRC() == ssrc) {
+    SetStartTimestamp(rtp_state.start_timestamp);
     rtp_sender_.SetRtpState(rtp_state);
     return true;
   }