Use 0 to disable NAT received processing and 1 to enable
NAT received processing. Default is 0.
If nat_received_processing is enabled, and received= tag
is in the Via header of the 200 OK response from a
REGISTER, the IP address in the received= tag is used
instead of the nat_address in the Contact header. If this
switch occurs, the phone unregisters the old IP address
and reregisters with the new IP address.