[Reviewer: Mike] Use Server-Assignment-Type UNREGISTERED rather than NO_ASSIGNMENT when no IMPI available

Mike,

Please can you review this fix to homestead?  Previously, we used NO_ASSIGNMENT when no private ID was available, but this is actually the wrong type - you must already be registered to this S-CSCF and a private ID must be provided.  Instead, UNREGISTERED_USER is the correct type to use in this scenario.

I've tested live and fixed up UT.

Thanks,

Matt