net: hns3: add arp proxy switch in ethtool

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8GQDK


CVE: NA

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To use arp proxy more conviency, add an arp proxy switch in ethool. Use
followed command to open or close arp proxy:
ethtool --set-priv-flags <device_name> roh_arp_proxy_enable <on/off>

Use followed command to find current state of arp proxy switch:
ethtool --show-priv-flags <device_name>

The results are showed as followed:
...
roh_arp_proxy_enable: on

Upstream: Yes
Bugfix or Feature: Feature
AR20230919193847

Signed-off-by: Peiyang Wang <wangpeiyang1@huawei.com>