Websocket server sends masked frames

[pjw]

https://github.com/apache/celix/blob/afedd8cc04a085df3a15c49718a8f9747ab1aca4/bundles/pubsub/pubsub_admin_websocket/src/pubsub_websocket_topic_sender.c#L332

At the above location mg_websocket_write() should be used when the connection is a server.