Move the parsing part of radioshack-dmm into a separate protocol
parser, following the model from hardware/common/dmm.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
The packet mode byte is akin to a signature. If that is invalid, there's
no point in calculating the checksum, so check the mode first.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>