Let iwm(4) use per-Tx-queue interface timers to ensure that the interface

Let iwm(4) use per-Tx-queue interface timers to ensure that the interface
watchdog will trigger a device timeout if a particular Tx queue gets stuck
while other Tx queues keep working.

The Linux driver is using a similar workaround for "stuck queues".
I have only observed this problem on iwx(4) hardware but it won't hurt
to add this workaround to iwm(4) as well.