net: hns: Fix loopback test failed at copper ports

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

When doing a loopback test at copper ports, the serdes loopback
and the phy loopback will fail, because of the adjust link had
not finished, and phy not ready.

Add sleep between adjust link and test process to fix it.

Feature or Bugfix:Bugfix

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Reviewed-by: lipeng <lipeng321@huawei.com>
Reviewed-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>