Fix static ucastrate for ath_rate_sample.
Fix static ucastrate for ath_rate_sample.

* Pull out the static rix stuff into a different function
* I know this may slightly drop performance, but check if a static
  rix is needed before each packet TX.

* Whilst I'm at it, add a little extra debugging to the rate
  control stuff to make it easier to follow what's going on.

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