NFSv4: More CLOSE/OPEN races

If an OPEN RPC call races with a CLOSE or OPEN_DOWNGRADE so that it
updates the nfs_state structure before the CLOSE/OPEN_DOWNGRADE has
a chance to do so, then we know that the state->flags need to be
recalculated from scratch.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>