net/phy: micrel: Disable asymmetric pause for KSZ9031

The KSZ9031 appears to suffer from the same hardware bug as described
for the KSZ9021 in commit 32fcafbc
("net/phy: micrel: Disable asymmetric pause for KSZ9021")
you have to unplug the cable and plug it back to get it to work.

Remove the SUPPORTED_Asym_Pause flag for the KSZ9031 to fix this.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>