LanTcpPlugin broadcasts a TransportDisabledEvent if it fails to bind key agreement socket
TcpPlugin#tryToClose(ServerSocket) broadcasts a TransportDisabledEvent, apparently as a convenience because the enabled/disabled state of the plugin is defined by whether a server socket is bound and the socket can be closed in several places. But LanTcpPlugin calls this method if it fails to bind a server socket for key agreement, wrongly broadcasting an event.
TorPlugin copies TcpPlugin's tryToClose() method. We should probably clean that up too, as TorPlugin will soon have other server sockets for rendezvous connections and we don't want to broadcast an event when they're closed.
Related to #1572.