ovl: update of dentry revalidate flags after copy up

ovl: update of dentry revalidate flags after copy up

[ Upstream commit b07d5cc93e1b28df47a72c519d09d0a836043613 ]

After copy up, we may need to update d_flags if upper dentry is on a
remote fs and lower dentries are not.

Add helpers to allow incremental update of the revalidate flags.

Fixes: bccece1ead36 ("ovl: allow remote upper")
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>