MonitorWorker::call_run_one_tick() called more often than intended

The delayed call which checks if a monitor should run a tick is not canceled when stopping monitor (e.g. for reconfiguration). If the monitor thread then starts again, another delayed call starts in addition to the one already scheduled. MonitorWorker::call_run_one_tick() is thus ran twice per 100ms. I.e. each time the monitor is restarted an additional delayed call is added.