iwlwifi: fix dual-mode scanning

The recent scanning code shuffle accidentally
moved the SCAN_HW bit setting _after_ the PAN
parameters are modified, which means that they
don't take the scan into account -- fix that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>