net: phylink: fix link mode modification in PHY mode

Modifying the link settings via phylink_ethtool_ksettings_set() and
phylink_ethtool_set_pauseparam() didn't always work as intended for
PHY based setups, as calling phylink_mac_config() would result in the
unresolved configuration being committed to the MAC, rather than the
configuration with the speed and duplex setting.

This would work fine if the update caused the link to renegotiate,
but if no settings have changed, phylib won't trigger a renegotiation
cycle, and the MAC will be left incorrectly configured.

Avoid calling phylink_mac_config() unless we are using an inband mode
in phylink_ethtool_ksettings_set(), and use phy_set_asym_pause() as
introduced in 4.20 to set the PHY settings in
phylink_ethtool_set_pauseparam().

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