fix bug

manager.go

@@ -25,6 +25,7 @@ func NewManager(tun io.ReadWriter) *Manager {
 		accept:        make(chan *DataFrame, 1024),
 		newConnection: make(chan *Connection),
 		delConnection: make(chan *Connection),
+		closed:        make(chan bool),
 		logger:        DefaultLogger,
 	}
 }