Add SocketFactoryInterface::Prepare and fix how symmetric NAT is determined

webrtc/p2p/stunprober/stunprober_dependencies.h

Index: webrtc/p2p/stunprober/stunprober_dependencies.h
diff --git a/webrtc/p2p/stunprober/stunprober_dependencies.h b/webrtc/p2p/stunprober/stunprober_dependencies.h
index 813a2f931c631432375ce67d832ec6970fb55e93..4e64df71ba6a7aceccfebbfaf6ea8f9efbbc5fca 100644
--- a/webrtc/p2p/stunprober/stunprober_dependencies.h
+++ b/webrtc/p2p/stunprober/stunprober_dependencies.h
@@ -35,10 +35,6 @@ class Socket : public ClientSocketInterface,
     return MapResult(socket_->Connect(addr));
   }
 
-  int Bind(const rtc::SocketAddress& addr) override {
-    return MapResult(socket_->Bind(addr));
-  }
-
   int SendTo(const rtc::SocketAddress& addr,
              char* buf,
              size_t buf_len,