cangw: add semantic check for checksum options
cangw: add semantic check for checksum options

The options to for adding checksums (-c or -x) can only be used in conjunction
with modifications (-m) applied to the routed CAN frames.

Signed-off-by: Andre Naujoks <227ae250b4ec1d98ba474022acd843e8770b0de1@googlemail.com>
Signed-off-by: Oliver Hartkopp <06a38fb2ed1a2d0a17f4f06761ac2e5ace5a31ab@hartkopp.net>

carloop/can-utils-osx,carloop/can-utils-osx