MINOR: lua: extend socket address to support non-IP families

MINOR: lua: extend socket address to support non-IP families

The HAProxy Lua socket respects the Lua Socket tcp specs. these specs
are a little bit limited, it not permits to connect to unix socket.

this patch extends a little it the specs. It permit to accept a
syntax that begin with "unix@", "ipv4@", "ipv6@", "fd@" or "abns@".