Change the AMRR TX rate control algorithm:
- Bookkeeping number of TX (counter1), and number of "fail to TX at
desired rate" (counter2), instead of bookkeeping number of TX at
each rate (old_counter[1-4]).
- Calculate "failure" and "success" conditions using 'counter1' and
'counter2', instead of only using 'old_counter1' and 'old_counter2'.
The mistake of the old way is that 'old_counter3' and 'old_counter4'
should also be taken as "fail to TX at desired rate".
- Nuke no longer needed macro after above changes.
This change is tested with acx(4). The testing result shows much
better TX performance under bad enviroment (e.g. lots of concrete
obstacles between STA and AP, long distance etc.).