wifi: iwlwifi: check validity of the FW API range

We assume that iwl_mac_cfg and iwl_rf_cfg instances has either
both ucode_api_min and ucode_api_max set, or neither.
Validate this assumption with a Kunit test.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250723094230.66502f3f4345.I661f347d3bb29994d8b2ec1d3f31f3383422d68a@changeid