net: hns3: Mask the packet statistics query when NIC is down

Update the HNS3_NIC_STATE_DOWN bit when NIC state changes.
When NIC is down, mask the packet statistics for querying
with ifconfig command. It's a common practice.

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>