net: dsa: mv88e6xxx: Unforce speed & duplex in mac_link_down()

Commit 64d47d5 ("net: dsa: mv88e6xxx: configure interface settings
in mac_config") removed forcing of speed and duplex from
mv88e6xxx_mac_config(), where the link is forced down, and left it only
in mv88e6xxx_mac_link_up(), by which time link is unforced.

It seems that (at least on 88E6190) when changing cmode to 2500base-x,
if the link is not forced down, but the speed or duplex are still
forced, the forcing of new settings for speed & duplex doesn't take in
mv88e6xxx_mac_link_up().

Fix this by unforcing speed & duplex in mv88e6xxx_mac_link_down().

Fixes: 64d47d5 ("net: dsa: mv88e6xxx: configure interface settings in mac_config")
Signed-off-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -768,6 +768,10 @@ static void mv88e6xxx_mac_link_down(struct dsa_switch *ds, int port,
 	if ((!mv88e6xxx_port_ppu_updates(chip, port) ||
 	     mode == MLO_AN_FIXED) && ops->port_sync_link)
 		err = ops->port_sync_link(chip, port, mode, false);
+
+	if (!err && ops->port_set_speed_duplex)
+		err = ops->port_set_speed_duplex(chip, port, SPEED_UNFORCED,
+						 DUPLEX_UNFORCED);
 	mv88e6xxx_reg_unlock(chip);
 
 	if (err)