When doing continual gathering, remove local candidates when a network is dropped.

webrtc/p2p/base/port.h

Index: webrtc/p2p/base/port.h
diff --git a/webrtc/p2p/base/port.h b/webrtc/p2p/base/port.h
index 95abe86464931e2d4029e0c5ac2c9770f998cc93..75b786fd0c5bedf6d6f6254819bdced97a47e135 100644
--- a/webrtc/p2p/base/port.h
+++ b/webrtc/p2p/base/port.h
@@ -358,6 +358,8 @@ class Port : public PortInterface, public rtc::MessageHandler,
     return ice_role_ == ICEROLE_CONTROLLED && connections_.empty();
   }
 
+  void OnNetworkInactive(const rtc::Network* network);
+
   rtc::Thread* thread_;
   rtc::PacketSocketFactory* factory_;
   std::string type_;