Reduce the number of alarms processed by the Profinet protocol stack in parallel

If the Profinet protocol stack processes the alarms by itself (and thus application is not involved), the number of alarms that can be processed in parallel should be reduced. This will limit the amount of "RTA Data Acknowledges" that the protocol stack generates in parallel. Not acknowledged alarms will be processed later in time based on a queueing mechanism.

This modification is only necessary in case of high network load and many IO-Devices, because otherwise in this case it might occur that some alarms are not acknowledged at all. The modification stabilizes the whole alarm handling process.