ehea: Add 64bit statistics

Switch to using ndo_get_stats64 to get 64bit statistics.

v3:
[cascardo] use rtnl_link_stats64 as port stats

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>