NFSv4: Fix nfs_clear_verifier_delegated() for delegated directories

NFSv4: Fix nfs_clear_verifier_delegated() for delegated directories

If the client returns a directory delegation, then look up all the child
dentries, and clear their 'verifier delegated' bit, unless subject to a
file delegation.

Similarly, if a file delegation is being returned, check if there is a
directory delegation before clearing a 'verifier delegated' bit.

Reported-by: Christoph Hellwig <hch@lst.de>
Fixes: 156b09482933 ("NFS: Request a directory delegation on ACCESS, CREATE, and UNLINK")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>