dlm_controld: ignore plocks until checkpoint time
    
    After our join confchg, we need to ignore plock messages
    until the point in time where the ckpt_node saves plock
    state (final start message received).  At that time we need
    to shift from ignoring plock messages to saving plock
    messages that will be applied on top of the plock state that
    is read from the checkpoint.  The code was not ignoring
    plock messages during the first stage of the process, which
    led to incorrect plock state.
    
    bz 623810
    
    Signed-off-by: David Teigland <teigland@redhat.com>