forcedeth: fix rx-work condition in nv_rx_process_optimized() too

The merge of my previous fix to forcedeth.c,
bcb5febb, lost an important hunk.

We need to fix nv_rx_process_optimized() too, as it contains duplicate logic.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jeff Garzik <jeff@garzik.org>