net: dsa: propagate resolved link config via mac_link_up()

Propagate the resolved link configuration down via DSA's
phylink_mac_link_up() operation to allow split PCS/MAC to work.

Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>