the previous calculation added 4 additional bytes to the buffers
when the length was already dividable by 4.
Signed-off-by: Christian Ambach <christian.ambach@deutschebahn.com>
Set up SPI slave transactions for entries in the SPI send queue.
Add a header to each SPI datagram that includes a CRC16,
the type and the size of the message that follows.
Does not act on received bytes (yet).
Signed-off-by: Christian Ambach <christian.ambach@deutschebahn.com>