net: hns3: add or modify comments

To explain some code, this patch adds some comments, and modifies or
merges some comments to make them more neat.

Signed-off-by: Guojia Liao <liaoguojia@huawei.com>
Signed-off-by: Zhongzhu Liu <liuzhongzhu@huawei.com>
Signed-off-by: Weihang Li <liweihang@hisilicon.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>