kernel - Enhance the FAIRQ ALTQ to use relative weightings

kernel - Enhance the FAIRQ ALTQ to use relative weightings

* Previously the FAIRQ altq specification guaranteed a bandwidth minimum
  for each queue but then used a fixed priority model for any excess
  bandwidth.

* Now the FAIRQ uses the minimum bandwidth specifications to also calculate
  relative weightings for any excess bandwidth, and no longer uses a fixed
  priority model.

* This results in a better apportionment of excess bandwidth and allows
  bandwidth specifications to also be used as a pure weighting specification
  if desired.

* Fix bandwidth calculation.  The decay was being executed on every packet
  instead of once a second.