net: dl2k: Use net_device_stats from struct net_device

Instead of using a private copy of struct net_device_stats in struct
netdev_private, use stats from struct net_device. Also remove the now
unnecessary .ndo_get_stats function and the #ifdef'ed increment of the
collisions16 counter which doesn't exist in struct net_device_stats.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>