net: hns3: Add Ethtool support to HNS3 driver

This patch adds the support of the Ethtool interface to
the HNS3 Ethernet driver. Various commands to read the
statistics, configure the offloading, loopback selftest etc.
are supported.

Signed-off-by: Daode Huang <huangdaode@hisilicon.com>
Signed-off-by: lipeng <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: Yisen Zhuang <yisen.zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>