There was a bug. Uplink MAC PDU were corrupted. It turns out
that at the end of the processing of an LDPC segment, the decoded
data is copied to the output buffer, but! with a wrong size, bigger
than it should. The bug I saw was with three segments: 0, 1, and 2.
Segment 1 was finished first, then 0, then 2. When copying segment
0, the beginning of segment 1 was overwritten with the end
of segment 1 (which contains non-data bytes but CRC bytes then 0s),
leading to a corrupted MAC PDU.

Let's copy only the decoded data bytes instead.