atl1c: 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 atl1c_adapter struct.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>