net: hns: Fix loopback test failed at copper ports

[ Upstream commit 2e1f164861e500f4e068a9d909bbd3fcc7841483 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>