net: hns3: refactor function hns3_fill_skb_desc to simplify code

The function hns3_fill_skb_desc is hard to read, this patch
extract 2 functions and add new a struct data to simplify the
code and Improve readability.

Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>