forcedeth: napi - handle all processing

The napi poll routine has been modified to handle all interrupt events
and process them accordingly. Therefore, the ISR will now only schedule
the napi poll and disable all interrupts instead of just disabling rx
interrupt.

Signed-off-by: Ayaz Abdulla <aabdulla@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>