net: ethoc: Account for duplex changes

ethoc_mdio_poll() which is our PHYLIB adjust_link callback does nothing,
we should at least react to duplex changes and change MODER accordingly.
Speed changes is not a problem, since the OpenCores Ethernet core seems
to be reacting okay without us telling it.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>