The DDS Writer was expecting the user to provide the serialized key
on DISPOSE/UNREGISTER operations. The user should have no direct
interaction with the serialized key.
The operation flow was changed to expect the normal payload from the
user, push it to the Key Holder, and the calculate the serialized key.
The stage that was responsible for simutanously pushing the input to
payload memory and/or the Key Holder was simplified, and the decode
error signal of the Key Holder is now handled.
The last two changes (simplified stage and decode error handling)
were also ported to the DDS Reader.
