ovl: add flag for upper in ovl_entry

For rename, we need to ensure that an upper alias exists for hard links
before attempting the operation.  Introduce a flag in ovl_entry to track
the state of the upper alias.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/dir.c

@@ -156,6 +156,7 @@ static void ovl_instantiate(struct dentry *dentry, struct inode *inode,
 			    struct dentry *newdentry, bool hardlink)
 {
 	ovl_dentry_version_inc(dentry->d_parent);
+	ovl_dentry_set_upper_alias(dentry);
 	if (!hardlink) {
 		ovl_inode_update(inode, newdentry);
 		ovl_copyattr(newdentry->d_inode, inode);