Rename RtpRtcp::Configuration::media_send_ssrc to local_media_ssrc

The name media_send_ssrc makes less sense when used mostly for the
RtcpReceiver functionality.

The old member is still there and used as a fallback. That will be
cleaned away after downstream code is fixed.

Bug: webrtc:10774
Change-Id: I4ec18db76910f31dfe76bc9b137ffe89220d3fa8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/149836
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28923}
diff --git a/audio/channel_send.cc b/audio/channel_send.cc
index d729b9f..876ee69 100644
--- a/audio/channel_send.cc
+++ b/audio/channel_send.cc
@@ -701,7 +701,7 @@
   configuration.extmap_allow_mixed = extmap_allow_mixed;
   configuration.rtcp_report_interval_ms = rtcp_report_interval_ms;
 
-  configuration.media_send_ssrc = ssrc;
+  configuration.local_media_ssrc = ssrc;
 
   _rtpRtcpModule = RtpRtcp::Create(configuration);
   _rtpRtcpModule->SetSendingMediaStatus(false);