net: dsa: mv88e6xxx: configure interface settings in mac_config

Only configure the interface settings in mac_config(), leaving the
speed and duplex settings to mac_link_up to deal with.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>