net: phy: phylink: Use PHY device interface if N/A

We may not always be able to resolve a correct phy_interface_t value before
actually connecting to the PHY device, when that happens, just have
phylink_connect_phy() utilize what the PHY device/driver provided.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>