Non volatile data handling: Give the host application the possibility to signal to the stack that non volatile data has been written

Currently when the stack receives a service (e.g. set attribute single) from the network addressing an attribute that is of type "non volatile" (e.g. TCP/IP Interface object's attribtue 3) it does the following:

1. Check the parameter value that shall be written for its validity
2. Send the service response to the network
3. Send an indication to the host application to indicate the new attribute value so that it can be stored in non volatile memory.

This approach has a big disadvantage: The service response in sent to the network before the attribute data can be stored by the application. Actually, the service response shall be sent NOT before the attribtue data is stored.