nfs: Subsequent READDIR calls should carry non-zero cookieverifier

nfs: Subsequent READDIR calls should carry non-zero cookieverifier

[ Upstream commit ee3707ae2c1f1327ad5188836b7ab62ed2c93b28 ]

If the loop in nfs_readdir_xdr_to_array() runs more than once, subsequent
READDIR RPCs may wrongly carry a zero cookie verifier and non-zero cookie.
Make sure subsequent calls to READDIR carry the cookie verifier returned
by the first call.

Signed-off-by: Nagendra S Tomar <natomar@microsoft.com>
Fixes: b593c09f83a2 ("NFS: Improve handling of directory verifiers")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>