cls_cgroup: Fix oops when user send improperly 'tc filter add' request

I found a bug in cls_cgroup_change() in cls_cgroup.c.
cls_cgroup_change() expected tca[TCA_OPTIONS] was set from user space properly,
but tc in iproute2-2.6.29-1 (which I used) didn't set it.

In the current source code of tc in git, it set tca[TCA_OPTIONS].

  git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git

If we always use a newest iproute2 in git when we use cls_cgroup, 
we don't face this oops probably.
But I think, kernel shouldn't panic regardless of use program's behaviour. 
Signed-off-by: Minoru Usui <usui@mxm.nes.nec.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_cgroup.c

@@ -167,6 +167,9 @@ static int cls_cgroup_change(struct tcf_proto *tp, unsigned long base,
 	struct tcf_exts e;
 	int err;
 
+	if (!tca[TCA_OPTIONS])
+		return -EINVAL;
+
 	if (head == NULL) {
 		if (!handle)
 			return -EINVAL;