s4-lib/socket: Allocate a the larger sockaddr_un and not just a sockaddr_in in unixdo...

s4-lib/socket: Allocate a the larger sockaddr_un and not just a sockaddr_in in unixdom_get_my_addr()

This caused crashes in _tsocket_address_bsd_from_sockaddr() when we
read past the end of the allocation.

(similar to commit e9ae36e9683372b86f1efbd29904722a33fea083)

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10042

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Wed Jul 24 14:37:43 CEST 2013 on sn-devel-104