Propogate network-worker thread split to api

BUG=webrtc:5645

Review-Url: https://codereview.webrtc.org/1968393002
Cr-Commit-Position: refs/heads/master@{#12767}
diff --git a/webrtc/api/peerconnection.cc b/webrtc/api/peerconnection.cc
index 5284db3..dda0eeb 100644
--- a/webrtc/api/peerconnection.cc
+++ b/webrtc/api/peerconnection.cc
@@ -588,8 +588,9 @@
       factory_->CreateMediaController(configuration.media_config));
 
   session_.reset(
-      new WebRtcSession(media_controller_.get(), factory_->signaling_thread(),
-                        factory_->worker_thread(), port_allocator_.get()));
+      new WebRtcSession(media_controller_.get(), factory_->network_thread(),
+                        factory_->worker_thread(), factory_->signaling_thread(),
+                        port_allocator_.get()));
   stats_.reset(new StatsCollector(this));
 
   // Initialize the WebRtcSession. It creates transport channels etc.