Robustness against unexpected host behavior in handling object changes is insufficient

With V5.1, the object change response packet was changed. It now needs to be returned with full contents and the stack then takes over that data.

Therefore, the packet is now returned with a nonzero length.

Anway, if it is returned with zero length (as it would have been done in the old API), then no reply is sent on the bus and the underlying encapsulation session never gets cleaned up, so that no network communication is possible anymore after the first 8 or so requests.

Aso, this fixes the issue described with PSEIP-85. If, for example, a NV attribute does not effectively change, the stack callbacks are not called and no response is send on the network. For instance, try to write attribute 14 of the TimeSync objectsmultiple times in a row from the network side to the same value and experience missing response messages.