openonuAdapterGo - missing device reason update from flow removal after ONU reboot

regression tests in multipleOlt/Onu scenarios show problems in the internal adapter processing after ONU soft reboot: issue are parallel incoming requests to delete flows and to deactivate the ONU (ONU operational down). In this case it may occur that the VlanConfigFsm is already running (to delete the flow) while the ONU down deactivation comes in a bit later. In this system state the OLT adapter does not forward the OMCI frames anymore (OK - ONU is down), but the internal reset of the FSM seems to have some problem to discard the outstanding wait for OMCI response. Accordingly the flow removal is not correctly finished and the deviceReason response is not generated. Correct cancellation of running FSM's with incoming ONU down event must be assured.