NFS: Revert "NFS: Move the flock open mode check into nfs_flock()"

Commit e1293727

 "NFS: Move the flock open mode check into nfs_flock()"
changed NFSv3 behavior for flock() such that the open mode must match the
lock type, however that requirement shouldn't be enforced for flock().

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Cc: stable@vger.kernel.org # v4.12
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>