[Make-wifi-fast] Diagram of the ath9k TX path

[Toke Høiland-Jørgensen]

I finally finished my flow diagram of the ath9k TX path (corresponding
to the previous one I did for the mac80211 stack). In case anyone else
is interested, it's available here:

https://blog.tohojo.dk/2016/05/the-ath9k-tx-path.html

-Toke