- Try adjusting TX power as much as possible when doing the initial TX power

- Try adjusting TX power as much as possible when doing the initial TX power
  calibration.  Also the second TX power calibration happens 1 second after
  the initial TX power calibration.  if streams are pushed immediately after
  NIC is brought up, this makes thing work much better for most of the 4306
  BBP, whose default TX power seems to be far away from the max TX power.
- Add some experimental (commented out) code to force TX power downgrade.
- For parts whose MAC rev >= 5, if PHY error happens, try resetting NIC but
  keep 802.11 state machine untouched.  PHY error usually happens when you
  roam into a signal dark corner, originally even if you walk the NIC out of
  the signal dark corner, TX performance still sucks; after this change, TX
  performance will stay on the right rank.  Heavy beacon missing that is
  enough to trigger reassoc/rescan does not seem to happen even if in this
  signal dark corner.