Net drivers using phylink shouldn't mess with the link carrier
themselves and should let phylink manage it. The mvpp2 driver wasn't
following this best practice as the mac_config() function made calls to
change the link carrier state. This led to wrongly reported carrier link
state which then triggered other issues. This patch fixes this
behaviour.

But the PPv2 driver relied on this misbehaviour in two cases: for fixed
links and when not using phylink (ACPI mode). The later was fixed by
adding an explicit call to link_up(), which when the ACPI mode will use
phylink should be removed.

The fixed link case was relying on the mac_config() function to set the
link up, as we found an issue in phylink_start() which assumes the
carrier is off. If not, the link_up() function is never called. To fix
this, a call to netif_carrier_off() is added just before phylink_start()
so that we do not introduce a regression in the driver.

Fixes: 4bb04326 ("net: mvpp2: phylink support")
Reported-by: Russell King <linux@armlinux.org.uk>
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>