Reset the BWE when the network changes

webrtc/media/engine/webrtcvoiceengine.cc

 /*
  *  Copyright (c) 2004 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 2316 matching lines @@
 
   // SR may continue RR and any RR entry may correspond to any one of the send
   // channels. So all RTCP packets must be forwarded all send channels. VoE
   // will filter out RR internally.
   for (const auto& ch : send_streams_) {
     engine()->voe()->network()->ReceivedRTCPPacket(
         ch.second->channel(), packet->data(), packet->size());
   }
 }
 
+void WebRtcVoiceMediaChannel::OnBestConnectionChanged(

[stefan-webrtc, 2016/03/17 12:48:19]

What will happen when we're not using BUNDLE? It's probably not a good thing
that voice tears down the BWE if only the voice connection has changed.

[honghaiz3, 2016/03/23 19:55:40]

This is a very good point.
We are using one BWE for all media channels, right?
Then the choices are
1) reset BWE if one media connection's network changed, or 
2) reset BWE if all media connections's networks changed. 
Is option 2) better?
In most cases, the media connection should be using the same network anyway, so
option 1 and 2 may not have big differences. 

+    Connection* best_connection) {
+  call_->OnBestConnectionChanged(best_connection);
+}
+
 bool WebRtcVoiceMediaChannel::MuteStream(uint32_t ssrc, bool muted) {
   RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
   int channel = GetSendChannelId(ssrc);
   if (channel == -1) {
     LOG(LS_WARNING) << "The specified ssrc " << ssrc << " is not in use.";
     return false;
   }
   if (engine()->voe()->volume()->SetInputMute(channel, muted) == -1) {
     LOG_RTCERR2(SetInputMute, channel, muted);
     return false;
@@ skipping 195 matching lines @@
     }
   } else {
     LOG(LS_INFO) << "Stopping playout for channel #" << channel;
     engine()->voe()->base()->StopPlayout(channel);
   }
   return true;
 }
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VOICE