ether3: Use net_device_stats from struct net_device

struct net_device has its own struct net_device_stats member, so use
this one instead of a private copy in the ether1_priv struct. As the new
ndo_get_stats function would just return dev->stats we can omit it. This
patch also removes an incorrect memset of the stats on open.

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