TLP Packetizer/Depacketizer: Create unit-tests and avoid code duplication

[enjoy-digital]

The TLP Packetizers/Depacketizers are using specific classes for the 64/128/256/512-bit datapaths. It should be possible to simplify the code by creating a generic Packetizer/Depacketizer that would support all the supported data widths. Before doing this, unit-tests for the current implementations should be created and used to validate the new generic module.