net: hns3: fix a phy loopback fail issue

net: hns3: fix a phy loopback fail issue

[ Upstream commit f04bbcbf1e38d192e94bbfa126731a52332c40b1 ]

When phy driver does not implement the set_loopback interface,
phy loopback test will return -EOPNOTSUPP, and the loopback test
will fail. So when phy driver does not implement the set_loopback
interface, don't do phy loopback test.

Fixes: c9765a89d142 ("net: hns3: add phy selftest function")
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>