be2net: Maintain tx and rx counters in driver

For certain skews of the BE adapter, H/W Tx and Rx
counters could be common for more than one interface.
Add Tx and Rx counters in the adapter structure
(to maintain stats on a per interfae basis).

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