net: hns3: enable DCB when TC num is one and pfc_en is non-zero

Currently when TC num is one, the DCB will be disabled no matter if
pfc_en is non-zero or not.

This patch enables the DCB if pfc_en is non-zero, even when TC num
is one.

Signed-off-by: Yunsheng Lin <linyunsheng@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>