net: hns3: check 1000M half for hns3_ethtool_ops.set_link_ksettings

Hip08 SOC does not support 1000M half, this patch adds 1000M half
check for hns3_ethtool_ops.set_link_ksettings, so the user can not
set 1000M half by ethtool.

Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>