rate_limited_udp_socket fixes

include/libtorrent/udp_socket.hpp

@@ -120,6 +120,7 @@ namespace libtorrent
 		void set_rate_limit(int limit) { m_rate_limit = limit; }
 		bool can_send() const { return int(m_queue.size()) >= m_queue_size_limit; }
 		bool send(udp::endpoint const& ep, char const* p, int len, error_code& ec);
+		void close();
 
 	private:
 		struct queued_packet

src/udp_socket.cpp

@@ -588,3 +588,9 @@ void rate_limited_udp_socket::on_tick(error_code const& e)
 	}
 }
 
+void rate_limited_udp_socket::close()
+{
+	m_timer.cancel();
+	udp_socket::close();
+}
+