Extra padding in packet_utils.py (tunnel.py example)

In packet_utils.py, function make_packet, there is always at least one
padding byte added:

pkt = ''.join((packed_preamble, packed_access_code, make_header(L),

whiten(payload_with_crc), ‘\x55’))

Can anyone explain why this is necessary? We’ve found in our tests that
not only is this necessary, but sometimes we need to add more than one
padding byte in order to get better throughput; i.e. if we only add one
padding byte then the last byte of our transmission is still corrupted,
but if we add 2 all of a sudden things work better. (This is before
doing the padding to make sure 512 bytes at a time get sent across the
USRP). It’s definitely tied to specific packet payloads too.