BUG/MINOR: unix: Make sure we can transfer abns sockets on seamless reload.

BUG/MINOR: unix: Make sure we can transfer abns sockets on seamless reload.

When checking if a socket we got from the parent is suitable for a listener,
we just checked that the path matched sockname.tmp, however this is
unsuitable for abns sockets, where we don't have to create a temporary
file and rename it later.
To detect that, check that the first character of the sun_path is 0 for
both, and if so, that &sun_path[1] is the same too.

This should be backported to 1.8.