md-cluster: change array_sectors and update size are not supported

Currently, some features are not supported yet,
such as change array_sectors and update size, so
return EINVAL for them and listed it in document.

Reviewed-by: NeilBrown <[e-mail]>
Signed-off-by: Guoqing Jiang <[e-mail]>
Signed-off-by: Shaohua Li <[e-mail]>

Documentation/md-cluster.txt

···
  nodes are using the raid which is achieved by lock all bitmap
  locks within the cluster, and also those locks are unlocked
  accordingly.
+
+7. Unsupported features
+
+There are somethings which are not supported by cluster MD yet.
+
+- update size and change array_sectors.

drivers/md/md.c

···
 	if (err)
 		return err;
 
+	/* cluster raid doesn't support change array_sectors */
+	if (mddev_is_clustered(mddev))
+		return -EINVAL;
+
 	if (strncmp(buf, "default", 7) == 0) {
 		if (mddev->pers)
 			sectors = mddev->pers->size(mddev, 0, 0);
···
 	struct md_rdev *rdev;
 	int rv;
 	int fit = (num_sectors == 0);
+
+	/* cluster raid doesn't support update size */
+	if (mddev_is_clustered(mddev))
+		return -EINVAL;
 
 	if (mddev->pers->resize == NULL)
 		return -EINVAL;