iwlwifi: honour regulatory restrictions in scan code

When doing firmware-assisted scanning, iwlwifi drivers do not
honour the regulatory control code that might disable channels
that are enabled in the EEPROM, for example when the user is
visiting another country and adjusted the regulatory domain
accordingly. This patch fixes that.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>