iwlwifi: mvm: support Bz TX checksum offload

Support TX checksum offload for Bz devices, where we have full
checksum offload (NETIF_F_HW_CSUM) and the hardware doesn't
need to parse the IP headers or anything.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20211219132536.c0f44c98b36d.I75a688f3ac80cbe824c459ece4bb67843b9fce76@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>