iwlwifi: fw api: support new API for scan config cmd

The API was reduced to include only knowledge currently needed by the
FW scan logic, the rest is legacy.  Support the new, reduced version.

Using the old API with newer firmwares (starting from
iwlwifi-*-50.ucode, which implements and requires the new API version)
causes an assertion failure similar to this one:

[    2.854505] iwlwifi 0000:00:14.3: 0x20000038 | BAD_COMMAND

Signed-off-by: Ayala Beker <ayala.beker@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>