net: hns3: add wait until mac link down

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7D6IP


CVE: NA

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In some configure flow of hns3 driver, for example, change mtu, it will
disable MAC through firmware before configuration. But firmware disables
MAC asynchronously. The rx traffic may be not stopped in this case.

So fixes it by waiting until mac link is down.

Fixes: a9775bb6 ("net: hns3: fix set and get link ksettings issue")
Signed-off-by: Jie Wang <wangjie125@huawei.com>