acenic: use netstats in net_device structure

Use net_device_stats from net_device structure instead of local.
No need to memset it to 0, because it is allocated by kzalloc.

Signed-off-by: Paulius Zaleckas <paulius.zaleckas@teltonika.lt>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>