forcedeth: don't poll NV event 36

Polling doesn't seem to be necessary on my hardware, at
least I haven't seen any bad effects testing it a while.
Remove the polling so the CPU doesn't have to wake up a
hundred times per second.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>