Implement CAN datagram encoding
Change specification to 32 bit data length
Change data length to 32 bit

This allows to write pages bigger than the previous 64k maximum. That
was needed because we had controllers with 128k pages.
Remove leftover debug output
Rename badly named test
Switch the datagram encoder to 32 bit data length
Rename test group
Compute CRC correctly on 32 bit data length
Compute CRC correctly on multiple destinations

We were only computing CRC on the first destination node.
Extract datagram CRC computation in a function