Allow to have UAC and UAS for a dialog on the same sipapp

If we invite an entity on the same node and the same sipapp as the initiating entity we end up in the same dialog and there is no way to ack the invitation. The easiest way to fix it seems as to have those dialog ids separated.

I'm not sure this is the best solution because the usage of the same dialog id could make it possible to shortcut the request to be processed without actually sending it on the wire.