Should not advertise pubsub#multi-subscribe when disabled
Pubsub can be configured to allow or disallow multiple subscriptions (to nodes) from the same JID. Openfire, by default, allows for this. Support can be toggled by setting the property 'xmpp.pubsub.multiple-subscriptions'
When the feature is disabled, the feature namespace ('http://jabber.org/protocol/pubsub#multi-subscribe') should not be advertised via service discovery (but currently is).