net: mdio: add mdio45_ethtool_ksettings_get

There is a function in mdio for the old ethtool api gset.
We add a new function mdio45_ethtool_ksettings_get for the
new ethtool api glinksettings.

Signed-off-by: Philippe Reynes <tremyfr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>