ovl: store ovl_entry in inode->i_private for all inodes

ovl: store ovl_entry in inode->i_private for all inodes

Previously this was only done for directory inodes.  Doing so for all
inodes makes for a nice cleanup in ovl_permission at zero cost.

Inodes are not shared for hard links on the overlay, so this works fine.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Orabug: 26401569

(backport upstream commit 58ed4e70f253d80ed72faba7873dc11603b398bc)

Signed-off-by: Shan Hai <shan.hai@oracle.com>
Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>