NAT64: Rewrite remote IPv4 address in Contact or Route

[nanang]

When receiving SIP message within/creating dialog, PJSIP should rewrite the Contact (and first Route if it is an initial INVITE transaction) if it is using IPv4 address, as otherwise, PJSIP will send a new request (within dialog) to that IPv4 address.

Thanks Kyle Kurz for the report.

[ming]

Rewriting address shouldn't be necessary, since the IPv4 address will be synthesized to an IPv6 one.

For more details, please refer to:

• https://trac.pjsip.org/repos/wiki/IPv6#NAT64
• https://trac.pjsip.org/repos/ticket/2032: NAT64 support for IPv4 interoperability
• https://trac.pjsip.org/repos/ticket/1976: Support to generate a synthesized IPv6 address from IPv4 address
• https://trac.pjsip.org/repos/ticket/2198: SIP resolve to return IPv4 and IPv6 addresses if address family is unspecified