be2net: Get rid of net_device_stats from adapter.

adapter doesnot need to maintain a copy of net_device_stats.
Use the one already available in net_device. This patch takes care of the same.

Signed-off-by: Ajit Khaparde <ajitk@serverengines.com>
Signed-off-by: David S. Miller <davem@davemloft.net>