Input: iforce - do not combine arguments for iforce_process_packet()

Current code combines packet type and data length into single argument to
iforce_process_packet() and then has to untangle it. It is much clearer to
simply use separate arguments.

Tested-by: Tim Schumacher <timschumi@gmx.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>