net: hns3: stop napi polling when HNS3_NIC_STATE_DOWN is set

When calling napi_disable during reset down process, if NAPIF_STATE_MISSED
is set, napi_complete will call __napi_schedule to do the polling again.
So this patch uses HNS3_NIC_STATE_DOWN to ensure the polling is not
scheduled again.

Also, when napi_complete returns true, it means polling is scheduled
again, it is not neccssary to enable the interrupt.

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