em(4): Reduce TX interrupt rate and device's TX desc write requests

[Sepherosa Ziehau]

Please review or test following patch:
http://leaf.dragonflybsd.org/~sephe/0001-em-4-Reduce-TX-interrupt-rate-and-device-s-TX-desc.patch

I plan to commit it before next week.

Best Regards,
sephe

-- 
Live Free or Die