net: hns3: move DMA map into hns3_fill_desc

To solve the L3 checksum error problem which happens when driver
does not clear L3 checksum, DMA map should be done after calling
skb_cow_head.

This patch moves DMA map into hns3_fill_desc to ensure that DMA
map is done after calling skb_cow_head.

Fixes: 76ad4f0e ("net: hns3: Add support of HNS3 Ethernet Driver for hip08 SoC")
Signed-off-by: Fuyun Liang <liangfuyun1@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>