net: hns: Fix loopback test failed at copper ports

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.

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

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>