net: hns3: add support for external loopback test

net: hns3: add support for external loopback test

[ Upstream commit 04b6ba143521f4485b7f2c36c655b262a79dae97 ]

This patch add support for external loopback test.
The successful test need the link is up with duplex full. The
driver do external loopback first, and then the whole offline
test.

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 8e6b9c6ea5a5 ("net: hns3: fix an interrupt residual problem")
Signed-off-by: Sasha Levin <sashal@kernel.org>