net/phy: micrel: Disable asymmetric pause for KSZ9021

Phyter KSZ9021 has hardware bug. If asymmetric pause is enabled,
then it is necessary to disconnect and then reconnect the ethernet
cable to get the phyter working. The solution is to disable the
asymmetric pause.

Signed-off-by: Vlastimil Kosar <ikosar@fit.vutbr.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>