net: dsa: rtl8366rb: Implement setting up link on CPU port

We auto-negotiate most ports in the RTL8366RB driver, but
the CPU port is hard-coded to 1Gbit, full duplex, tx and
rx pause.

This isn't very nice. People may configure speed and
duplex differently in the device tree.

Actually respect the arguments passed to the function for
the CPU port, which get passed properly after Russell's
patch "net: dsa: realtek: add phylink_get_caps implementation"

After this the link is still set up properly.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>