cifs: fix set of group SID via NTSD xattrs

'setcifsacl -g <SID>' silently fails to set the group SID on server.

Actually, the bug existed since commit 438471b6 ("CIFS: Add support
for setting owner info, dos attributes, and create time"), but this fix
will not apply cleanly to kernel versions <= v5.10.

Fixes: 3970acf7 ("SMB3: Add support for getting and setting SACLs")
Cc: stable@vger.kernel.org # 5.11+
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>