Convert net80211 over to using if_transmit for the dispatch from the
upper layer(s).

This eliminates the if_snd queue from net80211. Yay!

This unfortunately has a few side effects:

• It breaks ALTQ to net80211 for now - sorry everyone, but fixing parallelism and eliminating the if_snd queue is more important than supporting this broken traffic scheduling model. :-)

• There's no VAP and IC flush methods just yet - I think I'll add some NULL methods for now just as placeholders.

• It reduces throughput a little because now net80211 will drop packets rather than buffer them if the driver doesn't do its own buffering. This will be addressed in the future as I implement per-node software queues.

Tested:

• ath(4) and iwn(4) in STA operation