nfs4_acls: Add additional owner entry when mapping to NFS4 ACL with IDMAP_TYPE_BOTH

nfs4_acls: Add additional owner entry when mapping to NFS4 ACL with IDMAP_TYPE_BOTH

With IDMAP_TYPE_BOTH, all entries have to be mapped to group entries.
In order to have the file system reflect the owner permissions in the
POSIX modebits, create a second entry for the user. This will be mapped
to the "special owner" entry.

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>
(cherry picked from commit b796119e2df38d1935064556934dd10da6f3d339)