NFSv4: nfs4_copy_delegation_stateid() must fail if the delegation is invalid

NFSv4: nfs4_copy_delegation_stateid() must fail if the delegation is invalid

BugLink: http://bugs.launchpad.net/bugs/1637510
commit aa05c87f23efe417adc7ff9b4193b7201ec0dd79 upstream.

We must not allow the use of delegations that have been revoked or are
being returned.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Fixes: 869f9dfa4d6d ("NFSv4: Fix races between nfs_remove_bad_delegation()...")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Tested-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>