net: hns3: don't allow vf to enable promisc mode

VF can receive packets of other functions when in promisc
mode. It's not safe, so don't allow VF to enable promisc
mode.

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>