ovl: Treat metacopy dentries as type OVL_PATH_MERGE

Right now OVL_PATH_MERGE is used only for merged directories.  But
conceptually, a metacopy dentry (backed by a lower data dentry) is a merged
entity as well.

So mark metacopy dentries as OVL_PATH_MERGE and ovl_rename() makes use of
this property later to set redirect on a metacopy file.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/util.c

@@ -134,7 +134,8 @@ enum ovl_path_type ovl_path_type(struct dentry *dentry)
 		 */
 		if (oe->numlower) {
 			type |= __OVL_PATH_ORIGIN;
-			if (d_is_dir(dentry))
+			if (d_is_dir(dentry) ||
+			    !ovl_has_upperdata(d_inode(dentry)))
 				type |= __OVL_PATH_MERGE;
 		}
 	} else {