SIP resolve to return IPv4 and IPv6 synthesized addresses for IPv4 address literals

[ming]

When calling pjsip_resolve() on an IPv4 address, we will return both the IPv4 address and its synthesized IPv6 address (if any).

Note that since pjsip_resolve() has no information of the NAT64 mode nor the bound transport, it will still return the IPv6 address.

See also ticket #1976.

[ming]

In 5995:

Fixed #2198: SIP resolve to return both IPv4 and IPv6 synthesized addresses (if any) for IPv4 address literals.

• Also included in this changeset: ipv6 option of sample pjsua_app will now try IPv6 STUN, bind the account to IPv6 transport and set the IPv6 media

[ming]

In 5998:

Re #2198: Fixed wrong check that can return both IPv4 and IPv6 addresses

[ming]

In 6025:

Re #2198:

• Do not return IPv6 address for loop transport
• Fixed failed PJSIP test because of result count mismatch due to the additional IPv6 address