close method
Stops the listener. With force, open connections are dropped
immediately.
Implementation
@override
Future<void> close({bool force = false}) async {
final server = _server;
final sniServer = _sniServer;
_server = null;
_sniServer = null;
if (server != null) await server.close(force: force);
if (sniServer != null) await sniServer.close();
}