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_cbq.c b/net/sched/sch_cbq.c
index bb7e4cc..79f081e 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -1156,7 +1156,7 @@
 
 	r = nla_data(tb[TCA_CBQ_RATE]);
 
-	q->link.R_tab = qdisc_get_rtab(r, tb[TCA_CBQ_RTAB]);
+	q->link.R_tab = qdisc_get_rtab(r, tb[TCA_CBQ_RTAB], extack);
 	if (!q->link.R_tab)
 		return -EINVAL;
 
@@ -1484,7 +1484,7 @@
 
 		if (tb[TCA_CBQ_RATE]) {
 			rtab = qdisc_get_rtab(nla_data(tb[TCA_CBQ_RATE]),
-					      tb[TCA_CBQ_RTAB]);
+					      tb[TCA_CBQ_RTAB], extack);
 			if (rtab == NULL)
 				return -EINVAL;
 		}
@@ -1537,7 +1537,8 @@
 	if (!tb[TCA_CBQ_WRROPT] || !tb[TCA_CBQ_RATE] || !tb[TCA_CBQ_LSSOPT])
 		return -EINVAL;
 
-	rtab = qdisc_get_rtab(nla_data(tb[TCA_CBQ_RATE]), tb[TCA_CBQ_RTAB]);
+	rtab = qdisc_get_rtab(nla_data(tb[TCA_CBQ_RATE]), tb[TCA_CBQ_RTAB],
+			      extack);
 	if (rtab == NULL)
 		return -EINVAL;