Allow to turn RtcpTransciever on and off at runtime.

Bug: webrtc:8239
Change-Id: I8678d1ee9cd0da194a1243d40b508bb62cb3f257
Reviewed-on: https://webrtc-review.googlesource.com/60180
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22311}

modules/rtp_rtcp/source/rtcp_transceiver_config.h

@@ -80,6 +80,8 @@ struct RtcpTransceiverConfig {
   //
   // Tuning parameters.
   //
+  // Initial state if |outgoing_transport| ready to accept packets.
+  bool initial_ready_to_send = true;
   // Delay before 1st periodic compound packet.
   int initial_report_delay_ms = 500;