net: ethoc: implement ethtool get registers

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>