Revert "NFSv4: Remove incorrect check in can_open_delegated()"

This reverts commit 4e379d36.

This commit opens up a race between the recovery code and the open code.

Reported-by: Olga Kornievskaia <aglo@umich.edu>
Cc: stable@vger.kernel # v4.0+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>