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.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>