mac: Only use one CRC engine for Checker #183
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This probably never worked, but it certainly doesn't work right now
We don't need 4 crc engines for checking, we can use a single one, blank out the "invalid" data bytes and check it against a precomputed expected result
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As we have a certain crc value for a complete valid packet, additional 0 bytes lead to a predictable new crc value. Thus, for reception, we can only use a single, wide, engine and blank out the invalid bytes. Then compare it against a precomputed expected crc value for this last_be value.
To be certain that this works, add a test to verify it.
While using the test, I noticed that 16 bit support with last_be is completely broken.
64 bits also don't work with the test case, as a new packet can arrive which the old one isn't fully processed in checker, but this might not be a real issue on hardware.