net: hns3: avoid mult + div op in critical data path

This patch uses shift offset to avoid doing mult and div operation.

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