nfsd: Add support for CLAIM_DELEG_CUR_FH to the NFSv4.1/4.2 Open

The Linux NFSv4.1/4.2 client now uses the CLAIM_DELEG_CUR_FH
variant of the Open operation when delegations are recalled and
the client has a local open of the file. This patch adds
support for this variant of Open to the NFSv4.1/4.2 server.

This patch only affects mounts from Linux clients when delegations
are enabled on the server.

(cherry picked from commit b3d4c70dc60f1913f2363751b905b562c39ca126)