[Serusers] fix_nated_contact onreply

[samuel]

I have seen lots of default config files where in the reply route only
after checking the message (client_nat_test(1)) fix_nated is called.
Why is not called when the NAT flag is set upong lookup_XX?

In ser-oob I think the reply_route should include the case of a user
called behind a NAT and the reply is not fixed due to some router in
the middle. Will it hurt including fix_nated_contact in the case of
checking the flag?

Friday thoughts...

Samuel