nfsd: update create verifier comment

I don't know if that Solaris behavior matters any more or if it's still
possible to look up that bug ID any more.  The XFS behavior's definitely
still relevant, though; any but the most recent XFS filesystems will
lose the top bits.
Reported-by: Frank S. Filz <ffilzlnx@mindspring.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/vfs.c

@@ -1411,7 +1411,8 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 	if (nfsd_create_is_exclusive(createmode)) {
 		/* solaris7 gets confused (bugid 4218508) if these have
-		 * the high bit set, so just clear the high bits. If this is
+		 * the high bit set, as do xfs filesystems without the
+		 * "bigtime" feature.  So just clear the high bits. If this is
 		 * ever changed to use different attrs for storing the
 		 * verifier, then do_open_lookup() will also need to be fixed
 		 * accordingly.