net: hns3: fix for getting wrong link mode problem

Fixed link mode is returned by hns3_get_link_ksettings. It is
unreasonable.

This patch fixes it by adding some related functions to get link
mode from hardware.

Signed-off-by: Fuyun Liang <liangfuyun1@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>