Merge branch 'net_sched-sch_sfq-reject-limit-of-1'

Octavian Purdila says:

====================
net_sched: sch_sfq: reject limit of 1

The implementation does not properly support limits of 1. Add an
in-kernel check, in addition to existing iproute2 check, since other
tools may be used for configuration.

This patch set also adds a selfcheck to test that a limit of 1 is
rejected.

An alternative (or in addition) we could fix the implementation by
setting q->tail to NULL in sfq_drop if this is the last slot we marked
empty, e.g.:

  --- a/net/sched/sch_sfq.c
  +++ b/net/sched/sch_sfq.c
  @@ -317,8 +317,11 @@ static unsigned int sfq_drop(struct Qdisc *sch, struct sk_buff **to_free)
                  /* It is difficult to believe, but ALL THE SLOTS HAVE LENGTH 1. */
                  x = q->tail->next;
                  slot = &q->slots[x];
  -               q->tail->next = slot->next;
                  q->ht[slot->hash] = SFQ_EMPTY_SLOT;
  +               if (x == slot->next)
  +                       q->tail = NULL; /* no more active slots */
  +               else
  +                       q->tail->next = slot->next;
                  goto drop;
          }
====================

Link: https://patch.msgid.link/20241204030520.2084663-1-tavip@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>