Add 16-bit network id to the candidate signaling.

webrtc/base/network.cc

Index: webrtc/base/network.cc
diff --git a/webrtc/base/network.cc b/webrtc/base/network.cc
index 4f3b91981e4f08cef9a318e1be96af00c54eece5..4780e2f88d463ce9a9862e9da9b74a8c04e324d7 100644
--- a/webrtc/base/network.cc
+++ b/webrtc/base/network.cc
@@ -286,6 +286,7 @@ void NetworkManagerBase::MergeNetworkList(const NetworkList& new_networks,
       // This network is new. Place it in the network map.
       merged_list.push_back(net);
       networks_map_[key] = net;
+      net->set_id(next_available_network_id_++);
       // Also, we might have accumulated IPAddresses from the first
       // step, set it here.
       net->SetIPs(kv.second.ips, true);