nfsd: correctly define v4.2 support attributes

commit 6d0ba043 upstream.

Even when security labels are disabled we support at least the same
attributes as v4.1.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>