Major overhaul:

Major overhaul:
o eliminate private state indexed by 802.11 rate codes; use the hal's
  rate tables directly to get the same info
o calculate a mask of operational rates to optimize lookups and checks
  (instead of using for loops and similar)
o optimize size bin operations
o ignore rates marked as "do not use" in the hal phy tables
o fix bug that caused upshifting to break in 11g once the rate dropped
  below 11Mb/s
o add more intelligent multi-rate tx schedules
o add support for 1/2 and 1/4 width channels
o add dev.ath.X.sample_stats sysctl to dump runtime statistics to the console
  (needs to go up to a user app)
o export more tuning knobs via sysctls (still a couple of magic constants)