tc: policing requires a rate estimator

Found that while trying average rate policing, it was possible to
request average rate policing without a rate estimator. This results
in no policing which is harmless but incorrect.

Since policing could be setup in two steps, need to check
in the kernel.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/act_police.c b/net/sched/act_police.c
index e19a026..c39f60c 100644
--- a/net/sched/act_police.c
+++ b/net/sched/act_police.c
@@ -182,6 +182,12 @@
 		R_tab = qdisc_get_rtab(&parm->rate, tb[TCA_POLICE_RATE]);
 		if (R_tab == NULL)
 			goto failure;
+
+		if (!est && !gen_estimator_active(&police->tcf_rate_est)) {
+			err = -EINVAL;
+			goto failure;
+		}
+
 		if (parm->peakrate.rate) {
 			P_tab = qdisc_get_rtab(&parm->peakrate,
 					       tb[TCA_POLICE_PEAKRATE]);