net: aquantia: fetch up to date statistics on ethtool request

This improves ethtool -S usage, where stats are now actual
on each request. Before that stats only were updated at service
timer period.

Tested-by: Nikita Danilov <ndanilov@aquantia.com>
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: Dmitry Bogdanov <dmitry.bogdanov@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>