Rework BusState handling according to new definition

The new definition for BusState "off" as linked below shall be respected by the firmware.

This will change the behavior of IP stack in such a way, that on transition "Bus on" to "Bus off" the IP stack will keep its IP parameterization active and e.g. Socket API services can be used by application. The Profinet Protocol stack is however not reachable by DCP in this state.