Revert the transmission packet queueing strategy changes. Clearly I missed
something while debugging this, although I never encountered any problems
on my test machines.
Also make one other minor change: jack up the TX reclaim threshold for
3c90xB adapters in order to stave off 'transmission error: 82' errors.
Document the existence of the tx reclaim register (for inspecting the
current reclaim threshold) in register window 5 (if_xlreg.h).