ehea: Fixing statistics

(Applied over Eric's "ehea: fix use after free" patch)

Currently ehea stats are broken. The bytes counters are got from
the hardware, while the packets counters are got from the device
driver. Also, the device driver counters are resetted during the
the down process, and the hardware aren't, causing some weird
numbers.

This patch just consolidates the packets and bytes on the device
driver.

Signed-off-by: Breno Leitao <leitao@linux.vnet.ibm.com>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>