net: sched: red: notify drivers about RED's limit parameter

RED qdisc's limit parameter changes the behaviour of the qdisc,
for instance if it's set to 0 qdisc will drop all the packets.

When replace operation happens and parameter is set to non-0
a new fifo qdisc will be instantiated and replace the old child
qdisc which will be destroyed.

Drivers need to know the parameter, even if they don't impose
the actual limit to be able to reliably reconstruct the Qdisc
hierarchy.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: John Hurley <john.hurley@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/pkt_cls.h

@@ -850,6 +850,7 @@ struct tc_red_qopt_offload_params {
 	u32 min;
 	u32 max;
 	u32 probability;
+	u32 limit;
 	bool is_ecn;
 	bool is_harddrop;
 	struct gnet_stats_queue *qstats;

net/sched/sch_red.c

@@ -166,6 +166,7 @@ static int red_offload(struct Qdisc *sch, bool enable)
 		opt.set.min = q->parms.qth_min >> q->parms.Wlog;
 		opt.set.max = q->parms.qth_max >> q->parms.Wlog;
 		opt.set.probability = q->parms.max_P;
+		opt.set.limit = q->limit;
 		opt.set.is_ecn = red_use_ecn(q);
 		opt.set.is_harddrop = red_use_harddrop(q);
 		opt.set.qstats = &sch->qstats;