drivers/net/phy: add connection between ethtool and phylib for PLCA

This patch adds the required connection between netlink ethtool and
phylib to resolve PLCA get/set config and get status messages.

Signed-off-by: Piergiorgio Beruto <piergiorgio.beruto@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>