Add an option to check websocket Origin header via

listen {
	websocket {
		allow-origin { *.example.net; }
	}
}

This allows you to limit websockets to a particular domain, IF the
user is using a normal browser.

Note that any non-browser (eg a websocket command line program) could
just spoof the Origin header, so for that case it doesn't really add
any security or real restriction.

include/struct.h

@@ -1993,6 +1993,7 @@ struct ConfigItem_listen {
 	WebServer *webserver;		/**< For the webserver module */
 	void (*start_handshake)(Client *client); /**< Function to call on accept() */
 	int websocket_options;		/**< Websocket options (for the websocket module) */
+	NameList *websocket_origin;	/**< List of permitted Origin */
 	int rpc_options;		/**< For the RPC module */
 };