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_++);

[pthatcher1, 2016/03/21 17:49:24]

Should we skip the 0-value if it rolls over?

[honghaiz3, 2016/03/22 16:30:03]

It is highly unlikely to roll over to 0. 
If a new network is generated once every 5 seconds, it would take 64000 * 5  =
320000 seconds to roll over. That's about 80 hours.  
Even if it does, having a network id 0 is still fine. 

       // Also, we might have accumulated IPAddresses from the first
       // step, set it here.
       net->SetIPs(kv.second.ips, true);