[Serusers] re-invite and nat proxy

[Richard]

Hi,

I ran into some issues with re-invite and nat.

Ser uses "lookup" location to load the flag of a NATted callee. Because
re-invite already knows the callee's contact, it uses loose-route. It
doesn't call "lookup". The problem is that if the callee is behind NAT, ser
can't tell.

Since the ruri of re-invite is already in the location table, I wonder if we
can have another function to find it in the location table and load the
flag. Does it make sense?

Thanks,
Richard