MEDIUM: uxst: make use of sock_unix_bind_receiver()

MEDIUM: uxst: make use of sock_unix_bind_receiver()

This removes all the AF_UNIX-specific code from uxst_bind_listener()
and now simply relies on sock_unix_bind_listener() to do the same
job. As mentionned in previous commit, the only difference is that
now an unlikely failure on listen() will not result in a roll back
of the temporary socket names since they will have been renamed
during the bind() operation (as expected). But such failures do not
correspond to any normal case and mostly denote operating system
issues so there's no functionality loss here.