Enable some DF-11 error correction

Fixing single bit errors in DF-11 is a bit dodgy because we have no way
to know for sure if the crc is supposed to be 0 or not - it could be any
value less than 80. Therefore, attempting to fix DF-11 errors can result
in a multitude of possible crc solutions, only one of which is correct.

Therefore, we should probably perform some sanity checks on corrected
DF-11's, before using the results. Perhaps check the ICAO against known
aircraft, and check IID against known good IID's.

That's a TODO.