[Reviewer Alex] Handle reREGISTER requests containing a challenge response

Alex

Can you review my fix to issue #833.  I've fixed at the S-CSCF as discussed in the issue and I've also updated Bono to set integrity-protected=ip-assoc-pending when appropriate.  I've tested by updating UTs and also spinning up a live system.  I haven't tested live with a Perimeta or done any AKA live tests as these would be fairly effort and probably not justified as we have good UT coverage of any flows that might have been affected by the change.

Mike
Worth mentioning that `ip-assoc-pending` and `tls-pending` are used if the flow has not already been authenticated?