net: sch: api: add extack support in qdisc_get_rtab

This patch adds extack support for the function qdisc_get_rtab which is
a common used function in the tc subsystem. Callers which are interested
in the receiving error can assign extack to get a more detailed
information why qdisc_get_rtab failed.

Cc: David Ahern <dsahern@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Alexander Aring <aring@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 65762d5..51be1b7 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1357,10 +1357,12 @@ static int htb_change_class(struct Qdisc *sch, u32 classid,
 
 	/* Keeping backward compatible with rate_table based iproute2 tc */
 	if (hopt->rate.linklayer == TC_LINKLAYER_UNAWARE)
-		qdisc_put_rtab(qdisc_get_rtab(&hopt->rate, tb[TCA_HTB_RTAB]));
+		qdisc_put_rtab(qdisc_get_rtab(&hopt->rate, tb[TCA_HTB_RTAB],
+					      NULL));
 
 	if (hopt->ceil.linklayer == TC_LINKLAYER_UNAWARE)
-		qdisc_put_rtab(qdisc_get_rtab(&hopt->ceil, tb[TCA_HTB_CTAB]));
+		qdisc_put_rtab(qdisc_get_rtab(&hopt->ceil, tb[TCA_HTB_CTAB],
+					      NULL));
 
 	if (!cl) {		/* new class */
 		struct Qdisc *new_q;