Timer and interrupt fixes:

* Be pickier with what kind of interrupts are acked to avoid the device to
  get out of sync with the driver state
* Set RX count threshhold to 1 (for NAPI interrupted mode), TX count
  threshold to 32.
* Set timer thresholds to current max (~16ms).
Signed-off-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NJeff Garzik <jeff@garzik.org>