net: hns3: add support for external loopback test

mainline inclusion
from mainline-v6.0-rc4
commit 04b6ba14
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5QIIF
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=04b6ba143521



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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>
Signed-off-by: Jiantao Xiao <xiaojiantao1@h-partners.com>
Reviewed-by: Jian Shen <shenjian15@huawei.com>
Reviewed-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>