net/hns:bugfix of ethtool -t phy self_test

net/hns:bugfix of ethtool -t phy self_test

BugLink: https://bugs.launchpad.net/bugs/1705712
This patch fixes the phy loopback self_test failed issue. when
Marvell Phy Module is loaded, it will powerdown fiber when doing
phy loopback self test, which cause phy loopback self_test fail.

Signed-off-by: Lin Yun Sheng <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 7fe5b914313ff67d71cb2b5aa4b850e0884e75dd)
Signed-off-by: dann frazier <dann.frazier@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>