mqprio: Avoid panic if no options are provided

Userspace may not provide TCA_OPTIONS, in fact tc currently does
so not do so if no arguments are specified on the command line.
Return EINVAL instead of panicing.
Signed-off-by: NThomas Graf <tgraf@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_mqprio.c

@@ -107,7 +107,7 @@ static int mqprio_init(struct Qdisc *sch, struct nlattr *opt)
 	if (!netif_is_multiqueue(dev))
 		return -EOPNOTSUPP;
 
-	if (nla_len(opt) < sizeof(*qopt))
+	if (!opt || nla_len(opt) < sizeof(*qopt))
 		return -EINVAL;
 
 	qopt = nla_data(opt);