iwlwifi: mvm: Add support for hidden network scan on 6GHz band

Add support for discovery of hidden networks on the 6GHz band,
by including the scan request direct SSIDs in the FW scan request
command:

- In case a short SSID matches one of the direct SSIDs in the scan
  request command, add the matching SSID in the same offset in the
  'direct_ssids' array.
- Otherwise, add the SSID in one of the available slots.

Additionally, as a preparation to handle hidden APs, refactor
iwl_mvm_umac_scan_cfg_channels_v6_6g() the function.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210802170640.ffb540a70212.Ia2bb9bc9435b833820bcc7dc30adcedb5a5a9869@changeid


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