Simulcast work to enable RID mux.

Rids can now be sent using rtp_sender.
Hooking up the rid values in the voice and video engine is still WIP.

Bug: webrtc:10074
Change-Id: I245c7ecb23b67fc0ba65caaa5dbb4fcfd60c81bb
Reviewed-on: https://webrtc-review.googlesource.com/c/114505
Commit-Queue: Amit Hilbuch <amithi@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Seth Hampson <shampson@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26092}

modules/rtp_rtcp/source/rtp_rtcp_impl.h

@@ -105,6 +105,8 @@ class ModuleRtpRtcpImpl : public RtpRtcp, public RTCPReceiver::ModuleRtpRtcp {
   // Configure SSRC, default is a random number.
   void SetSSRC(uint32_t ssrc) override;
 
+  void SetRid(const std::string& rid) override;
+
   void SetMid(const std::string& mid) override;
 
   void SetCsrcs(const std::vector<uint32_t>& csrcs) override;