[E1000E]: update netstats traffic counters realtime

formerly e1000/e1000e only updated traffic counters once every
2 seconds with the register values of bytes/packets. With newer
code however in the interrupt and polling code we can real-time
fill in these values in the netstats struct for users to see.

Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>