net: hns: bug fix about restart auto-negotiation

When set auto-negotiation off and duplex half, if run "ethtool -r ethX"
on port with phy, then the port will be failed to work. It should
forbid to start auto-negotiation when auto-negotiate is off. This
patch add the limited condition.

Reported-by: Jinchuang Tian <tianjinchuang1@huawei.com>
Signed-off-by: Daode Huang <huangdaode@hisilicon.com>
Reviewed-by: Yisen Zhuang <yisen.zhuang@huawei.com>
Reviewed-by: lipeng <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>