net: phylink: cleanup ksettings_set

We only need to fiddle about with the supported mask after we have
validated the user's requested parameters. Simplify and streamline the
code by moving the linkmode copy and update of the autoneg bit after
validating the user's request.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>