MEDIUM: socket: always properly use the sock_domain for requested families

MEDIUM: socket: always properly use the sock_domain for requested families

Now we make sure to always look up the protocol's domain for an address
family. Previously we would use it as-is, which prevented from properly
using custom addresses (which is when they differ).

This removes some hard-coded tests such as in log.c where UNIX vs UDP
was explicitly checked for example. It requires a bit of care, however,
so as to properly pass value 1 in the 3rd arg of the protocol_lookup()
for DGRAM stuff. Maybe one day we'll change these for defines or enums
to limit mistakes.