net: phy: let genphy_c45_read_abilities also check aneg capability

When using genphy_c45_read_abilities() as get_features callback we
also have to set the autoneg capability in phydev->supported.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>