net: sched: sfq: convert to qdisc drop reasons

net: sched: sfq: convert to qdisc drop reasons

Convert SFQ to use the new qdisc-specific drop reason infrastructure.

This patch demonstrates how to convert a flow-based qdisc to use the
new enum qdisc_drop_reason. As part of this conversion:

- Add QDISC_DROP_MAXFLOWS for flow table exhaustion
- Rename FQ_FLOW_LIMIT to generic FLOW_LIMIT, now shared by FQ and SFQ
- Use QDISC_DROP_OVERLIMIT for sfq_drop() when overall limit exceeded
- Use QDISC_DROP_FLOW_LIMIT for per-flow depth limit exceeded

The FLOW_LIMIT reason is now a common drop reason for per-flow limits,
applicable to both FQ and SFQ qdiscs.

Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://patch.msgid.link/177211345946.3011628.12770616071857185664.stgit@firesoul
Signed-off-by: Jakub Kicinski <kuba@kernel.org>