net: mvneta: mark as a legacy_pre_march2020 driver

mvneta provides mac_an_restart and mac_pcs_get_state methods, so needs
to be marked as a legacy driver. Marek spotted that mvneta had stopped
working in 2500base-X mode - thanks for reporting.
Reported-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -5275,6 +5275,7 @@ static int mvneta_probe(struct platform_device *pdev)
 
 	pp->phylink_config.dev = &dev->dev;
 	pp->phylink_config.type = PHYLINK_NETDEV;
+	pp->phylink_config.legacy_pre_march2020 = true;
 	pp->phylink_config.mac_capabilities = MAC_SYM_PAUSE | MAC_10 |
 		MAC_100 | MAC_1000FD | MAC_2500FD;