wifi: iwlwifi: mvm: fix netif csum flags

We shouldn't advertise arbitrary checksum flags since we had
to remove support for it due to broken hardware.

Fixes: ec18e7d4

 ("wifi: iwlwifi: mvm: use old checksum for Bz A-step")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20231017115047.e37327f1a129.Iaee86b00db4db791cd90adaf15384b8c87d2ad49@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>