vfs_glusterfs: Implement proper mashalling/unmarshalling of ACLs

vfs_glusterfs: Implement proper mashalling/unmarshalling of ACLs

Use the primitives available in Samba byteorder.h for implementing
proper (un)marshalling of ACL xattrs.
- Incorporated Raghavendra Talur's comments on v3

Signed-off-by: Anand Avati <avati@redhat.com>
Signed-off-by: Raghavendra Talur <rtalur@redhat.com>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Christopher R. Hertel <crh@samba.org>
Tested-by: Jose A. Rivera <jarrpa@redhat.com>
Autobuild-User(master): Simo Sorce <idra@samba.org>
Autobuild-Date(master): Fri Aug 16 20:34:51 CEST 2013 on sn-devel-104