net: phy: phylink: Report MoCA as PORT_BNC

Similarly to what PHYLIB already does, make sure that
PHY_INTERFACE_MODE_MOCA is reported as PORT_BNC.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>