[PATCH] ixp2000: use netif_rx_schedule_test

The sky2 driver introduced netif_rx_schedule_test().  This is
exactly what we need, so remove our local version of this function
(which was called netif_rx_schedule_prep_notup) and use the generic
one instead.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>