iwlwifi: pass txq to wake/stop queue

Instead of passing the txq->swq_id, pass the
txq struct directly to make sure that in the
future nobody will pass an invalid number.
Only three places actually change from using
the txq_id or the skb's queue_mapping to now
using txq->swq_id as well.

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