via-velocity: use netdev_alloc_skb

Use netdev_alloc_skb for rx buffer allocation. This sets skb->dev
and can be overriden for NUMA machines.

Change code to return new buffer rather than call by reference.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>