net/sched: sch_cake: avoid sync overhead when unlimited

net/sched: sch_cake: avoid sync overhead when unlimited

Skip inter-instance sync when no rate limit is configured, as it serves
no purpose and only adds overhead.

Fixes: 1bddd758bac2 ("net/sched: sch_cake: share shaper state across sub-instances of cake_mq")
Signed-off-by: Jonas Köppeler <j.koeppeler@tu-berlin.de>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://patch.msgid.link/20260226-cake-mq-skip-sync-bandwidth-unlimited-v1-1-01830bb4db87@tu-berlin.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>