pkt_sched: fix missing check for packet overrun in qdisc_dump_stab()

nla_nest_start() might return NULL, causing a NULL pointer dereference.

Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/sched/sch_api.c

···
 	struct nlattr *nest;
 
 	nest = nla_nest_start(skb, TCA_STAB);
+	if (nest == NULL)
+		goto nla_put_failure;
 	NLA_PUT(skb, TCA_STAB_BASE, sizeof(stab->szopts), &stab->szopts);
 	nla_nest_end(skb, nest);