Set the preferred DSCP value for Rtp data channel to be DSCP_AF41.

webrtc/media/base/fakemediaengine.h

Index: webrtc/media/base/fakemediaengine.h
diff --git a/webrtc/media/base/fakemediaengine.h b/webrtc/media/base/fakemediaengine.h
index d97bab3dc231a08f4579eb244480f0cc2dfb8ecb..dc547f8f10de17ba32a8d0ca7740968a7b8d993b 100644
--- a/webrtc/media/base/fakemediaengine.h
+++ b/webrtc/media/base/fakemediaengine.h
@@ -943,7 +943,8 @@ class FakeDataEngine : public DataEngineInterface {
  public:
   FakeDataEngine() : last_channel_type_(DCT_NONE) {}
 
-  virtual DataMediaChannel* CreateChannel(DataChannelType data_channel_type) {
+  virtual DataMediaChannel* CreateChannel(DataChannelType data_channel_type,
+                                          const MediaConfig& config) {
     last_channel_type_ = data_channel_type;
     FakeDataMediaChannel* ch = new FakeDataMediaChannel(this, DataOptions());
     channels_.push_back(ch);