fix a couple of problems if openais enables flow control:
    - the poll loop spins due to plocks being ready to process but being
      ignored due to the flow control; we need to remove the plock fd from
      the poll set when flow control is enabled (just like we do when the
      plock rate limiter is active)
    - we were not updating the flow control state from openais when
      flow control was enabled unless we received a cpg message; we need
      to update it periodically while blocked since we may not receive
      cpg messages from other nodes causing us to update the state