net_sched: Use struct_size() and flex_array_size() helpers

mainline inclusion
from mainline-v5.16-rc1
commit 69508d43
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6SFHJ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=69508d43334e3b09c344f662272bcf24a5b508ed

--------------------------------

Make use of the struct_size() and flex_array_size() helpers instead of
an open-coded version, in order to avoid any potential type mistakes
or integer overflows that, in the worse scenario, could lead to heap
overflows.

Link: https://github.com/KSPP/linux/issues/160


Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20210928193107.GA262595@embeddedor


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Conflicts:
	net/sched/sch_api.c

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: Liu Jian <liujian56@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>