Add void::RtcpFeedbackSenderInterface::SendCombinedRtcpPacket

This method sends arbitrary number rtp::RcpPackets into one or more IP packets.
It is implemented both in RtcpTranceiver and in RtpRtcp.

Change-Id: I00424ee2f1730ff98626f768846f4ac1ad864933

BUG: webrtc:10742
Change-Id: I00424ee2f1730ff98626f768846f4ac1ad864933
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/156240
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29430}

modules/rtp_rtcp/source/rtcp_transceiver_impl.h

@@ -63,6 +63,11 @@ class RtcpTransceiverImpl {
   void SendPictureLossIndication(uint32_t ssrc);
   void SendFullIntraRequest(rtc::ArrayView<const uint32_t> ssrcs);
 
+  // SendCombinedRtcpPacket ignores rtcp mode and does not send a compound
+  // message. https://tools.ietf.org/html/rfc4585#section-3.1
+  void SendCombinedRtcpPacket(
+      std::vector<std::unique_ptr<rtcp::RtcpPacket>> rtcp_packets);
+
  private:
   class PacketSender;
   struct RemoteSenderState;