net_sched: sch_sfq: use a temporary work area for validating configuration

[ Upstream commit 8c0cea59 ]

Many configuration parameters have influence on others (e.g. divisor
-> flows -> limit, depth -> limit) and so it is difficult to correctly
do all of the validation before applying the configuration. And if a
validation error is detected late it is difficult to roll back a
partially applied configuration.

To avoid these issues use a temporary work area to update and validate
the configuration and only then apply the configuration to the
internal state.

Signed-off-by: Octavian Purdila <tavip@google.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: b3bf8f63 ("net_sched: sch_sfq: move the limit validation")
Signed-off-by: Sasha Levin <sashal@kernel.org>