Consider the server IP address before trying to re-register with a new Contact when the REGISTER response contains different IP address

[bennylp]

Ticket #409 (from 0.8.0 milestone) adds the feature to automatically re-register the account if the Via address in the 200/OK response to REGISTER contains different address than the one being registered as Contact header.

This feature is intended to work with symmetric NATs.

However there are cases where this feature do not work very well. Some NAT in the middle might mess up with the SIP/SDP addresses, and eventhough the initial REGISTER request contains public address in the Via header, the router may change the Via header in the response back to the private IP, causing the client to re-register using the private IP.

[bennylp]

Done in r2316:

• we will not switch if the Contact and server IP are in public network but the address in Via header contains private IP

[nanang]

In r2325:

• added setting to disable this ticket (by setting allow_contact_rewrite to 2)