Add/remove receive streams with SSRC 0 from media channels

This enables creation and removal of receive streams with SSRC 0.
Several related methods, for example SetOutputVolume, still use 0 as a
special value.

Bug: webrtc:8694
Change-Id: I341e6bd6c981c9838997510d8d712ad2948f6460
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/152780
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Saurav Das <dinosaurav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#29398}
diff --git a/media/base/rtp_data_engine.h b/media/base/rtp_data_engine.h
index 60d5f55..e5f071d 100644
--- a/media/base/rtp_data_engine.h
+++ b/media/base/rtp_data_engine.h
@@ -72,6 +72,7 @@
   virtual bool RemoveSendStream(uint32_t ssrc);
   virtual bool AddRecvStream(const StreamParams& sp);
   virtual bool RemoveRecvStream(uint32_t ssrc);
+  virtual void ResetUnsignaledRecvStream();
   virtual bool SetSend(bool send) {
     sending_ = send;
     return true;