net: hns3: add debug messages to identify eth down cause

Some times just see the eth interface have been down/up via
dmesg, but can not know why the eth down. So adds some debug
messages to identify the cause for this.

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
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>