iwlwifi: always build swq_id as virtual queue ID

Previously, we used the swq_id's mechanism
to have AC and HW queue different only for
aggregation queues. To be able to fix a bug
with iPAN simply always build the swq_id as
ac | (hwq << 2) and remove the flag bit.

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