net: phylink: actually fix ksettings_set() ethtool call

Raju Lakkaraju reported that the below commit caused a regression
with Lan743x drivers and a 2.5G SFP. Sadly, this is because the commit
was utterly wrong. Let's fix this properly by not moving the
linkmode_and(), but instead copying the link ksettings and then
modifying the advertising mask before passing the modified link
ksettings to phylib.

Fixes: df0acdc5 ("net: phylink: fix ksettings_set() ethtool call")
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1q4eLm-00Ayxk-GZ@rmk-PC.armlinux.org.ukSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/phylink.c

@@ -2225,11 +2225,13 @@ int phylink_ethtool_ksettings_set(struct phylink *pl,
 
 	ASSERT_RTNL();
 
-	/* Mask out unsupported advertisements */
-	linkmode_and(config.advertising, kset->link_modes.advertising,
+	if (pl->phydev) {
+		struct ethtool_link_ksettings phy_kset = *kset;
+
+		linkmode_and(phy_kset.link_modes.advertising,
+			     phy_kset.link_modes.advertising,
 			     pl->supported);
 
-	if (pl->phydev) {
 		/* We can rely on phylib for this update; we also do not need
 		 * to update the pl->link_config settings:
 		 * - the configuration returned via ksettings_get() will come
@@ -2248,10 +2250,13 @@ int phylink_ethtool_ksettings_set(struct phylink *pl,
 		 *   the presence of a PHY, this should not be changed as that
 		 *   should be determined from the media side advertisement.
 		 */
-		return phy_ethtool_ksettings_set(pl->phydev, kset);
+		return phy_ethtool_ksettings_set(pl->phydev, &phy_kset);
 	}
 
 	config = pl->link_config;
+	/* Mask out unsupported advertisements */
+	linkmode_and(config.advertising, kset->link_modes.advertising,
+		     pl->supported);
 
 	/* FIXME: should we reject autoneg if phy/mac does not support it? */
 	switch (kset->base.autoneg) {