iwlwifi: invert the order of ssid list in scan cmd

The firmware inverts the order of ssid list of scan command, we
should invert the order before sending the command, in order to
get probe requests sent in wanted order.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>