net/hns:bugfix of ethtool -t phy self_test

This patch fixes the phy loopback self_test failed issue. when
Marvell Phy Module is loaded, it will powerdown fiber when doing
phy loopback self test, which cause phy loopback self_test fail.

Signed-off-by: Lin Yun Sheng <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>