net_sched: sch_fq: rework fq_gc() to avoid stack canary

net_sched: sch_fq: rework fq_gc() to avoid stack canary

Using kmem_cache_free_bulk() in fq_gc() was not optimal.

1) It needs an array.
2) It is only saving cpu cycles for large batches.

The automatic array forces a stack canary, which is expensive.

In practice fq_gc was finding zero, one or two flows at most
per round.

Remove the array, use kmem_cache_free().

This makes fq_enqueue() smaller and faster.

$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-79 (-79)
Function                                     old     new   delta
fq_enqueue                                  1629    1550     -79
Total: Before=24886583, After=24886504, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260204190034.76277-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>