vfs_gpfs: Implement special case for denying owner access to ACL

vfs_gpfs: Implement special case for denying owner access to ACL

In GPFS, it is not possible to deny ACL or attribute access through a
SPECIAL_OWNER entry. The best that can be done is mapping this to a
named user entry, as this one can at least be stored in an ACL. The same
cannot be done for inheriting SPECIAL_OWNER entries, as these represent
CREATOR OWNER entries, and the limitation of not being able to deny
owner access to ACL or attributes remains.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14032

Signed-off-by: Christof Schmitt <cs@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>