nfs4_acls: Implement fstat with DAC_CAP_OVERRIDE

nfs4_acls: Implement fstat with DAC_CAP_OVERRIDE

AT_EMTPY_PATH does not exist on AIX. Address this by implementing an
override for fstat.  Implement the new override function in nfs4_acls.c
since all stat functions with DAC_CAP_OVERRIDE will be moved there to
allow reuse by other filesystems.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15507

Signed-off-by: Christof Schmitt <cs@samba.org>
Reviewed-by: Björn Jacke <bjacke@samba.org>
(cherry picked from commit 05f1ee1ae2d8439af0ac9baf64ebba1a3374ea83)