net: stmmac: Use resolved link config in mac_link_up()

Convert the stmmac ethernet driver to use the finalised link parameters
in mac_link_up() rather than the parameters in mac_config().

Suggested-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>