mount: fix mnt_resort_siblings to work as described

We should add new entry _before_ first entry with less depth to sort in
descending order.

e.g: entries in list have depths [7,5,3], adding new entry m with depth
4 we would break list_for_each_entry loop on p with depth 3, before
patch we would get [7,5,3,4] after list_add, which is wrong.

Also we can relax "<=" check to "<" to avoid unnecessary reordering.
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/mount.c

@@ -446,10 +446,10 @@ static void mnt_resort_siblings(struct mount_info *tree)
 
 		depth = mnt_depth(m);
 		list_for_each_entry(p, &list, siblings)
-			if (mnt_depth(p) <= depth)
+			if (mnt_depth(p) < depth)
 				break;
 
-		list_add(&m->siblings, &p->siblings);
+		list_add_tail(&m->siblings, &p->siblings);
 		mnt_resort_siblings(m);
 	}