net: hns3: add support for RX completion checksum

In some cases (for example ip fragment), hardware will
calculate the checksum of whole packet in RX, and setup
the HNS3_RXD_L2_CSUM_B flag in the descriptor, so add
support to utilize this checksum.

Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>