[Serusers] Rewriting URI in the Contact field

[Maxim Sobolev]

Folks,

I need an advise on how to better implement one feature, which isn't
currently present in SER. We need to allow UAs behind NAT properly
register with the registrar - by "properly" I mean that host:port portion
of URI in Contact field should not be used, but host:port the request
came from should be used instead. By definition we know that those UAs
will support symmetric SIP signalling, so that this scheme will work just
fine.

In my opinion there are two ways to do it: either add new rewritecontact*
family of functions similar to rewritehost ones. or add a new flag for
the save() function. This is where I need your help - which implementation
looks better for you (or maybe you have even some better idea), since
we are really interested in inclusion of our changes into the mainline to
reduce our local hacks.

Regards,

Maxim