net: mvpp2: a port can be disabled even if we use the link IRQ

We had a check in the mvpp2_mac_link_down() function (called by phylink)
to avoid disabling the port when link interrupts are used. It turned out
the interrupt can still be used with the port disabled. We can thus
remove this check.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>