forcedeth: fix nic poll

The nic poll routine was missing the call to the optimized irq routine.
This patch adds the missing call for the optimized path.

See http://bugzilla.kernel.org/show_bug.cgi?id=7950

 for more information.

Signed-Off-By: Ayaz Abdulla <aabdulla@nvidia.com>

Signed-off-by: Jeff Garzik <jeff@garzik.org>