wifi: iwlwifi: cfg: reduce mac_type to u8

In theory, this should be 12 bits, but in practice all the
values we use now fit into 8 bits, so change the mac_type to
make room in struct iwl_dev_info.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250502155404.c17d56f4ae0f.I487c8df18aa33c46aa6813bf5aebb5a23da67600@changeid