NFSv4: Fix open recovery

NFSv4 open recovery is currently broken: since we do not clear the
state->flags states before attempting recovery, we end up with the
'can_open_cached()' function triggering. This again leads to no OPEN call
being put on the wire.

Reported-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org