Implement mechanism to be able to store remanent data

According to Profinet specification every Profinet device (IO Devices as well as IO Controllers) shall offer writable SNMP objects. These objects can be written and after a powercycle the written values need to be visible again.

In addition it is required to store NameOfStation and IP parameters set via DCP.

To support this the firmware needs

• an API to inform the user about parameters that need to be stored
• a defined way how to restore the data prior to Sycon.net database evaluation (enforce application controlled startup)
• fix size of packet shall be 8 KB (to have some reserve for future use)