fix obviously wrong check in decode_packet()

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Only process scrambled content in decode_packet()

When trying to run decke/drmdecrypt it did not work as expected.
After comparing the output of https://github.com/IvoNet/drmdecrypt
with decke's version a check for scrambled content was missing.

Originally this check is from:
https://github.com/marvin0815/drmdecrypt

Now decke's version is fast AND works :-)

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>