ipv6 address used as extip results in 127.0.0.1 being used

[smin-k]

Fix ethereum#29495.

Add a condition to the IP() function to check if ip4 is the local host.
Prefer ip6 over localhost.

[user@user]$ ./build/bin/geth --nodiscover --maxpeers 0 --nat extip:1050:0:0:0:5:600:300c:326b -goerli console
INFO [05-09|19:08:13.329] New local node record                    seq=1,715,165,299,988 id=3fe08aae98fe901d ip=1050::5:600:300c:326b udp=0 tcp=30303
INFO [05-09|19:08:13.330] Started P2P networking                   self="enode://097502837e94b3542b6d796f08fba193adc5c932e3d3875fb276e749aca4a39217fabc8fd34566581423329c61d49778d4f6bd563d6d3e3f8b3eacb64034aff1@[1050::5:600:300c:326b]:30303?discport=0"

[smin-k]

ethereum#29736