Unexpected interval between sync frames in IRT mode

When the firmware is configured for IRT operation and PTCP Sync Master, the syncframes might be sent in varying intervals. (e.g. 30ms/10ms) during startup phase. (First 10 seconds after BusOn) This will result in additional jitter of the syncronized slaves. In turn frames might be send at wrong times and already established ARs are arborted.

It is expected that sync frames are sent in constant interval as configured.