fix iwx(4) monitor mode

fix iwx(4) monitor mode

Monitor mode was broken by a recent firmware update. Two tweaks make
it work again:

1) The firmware does not like us sending the power-mode command while
in monitor mode and will panic, so simply don't do that.

2) We no longer add two queues while in monitor mode, just one queue
for frame injection. This queue's index will be 1, not 2. Make the
driver expect the correct index to prevent an error when monitor mode
is entered.

tested by jmc@ and myself on iwx ax200