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/include/net/gen_stats.h b/include/net/gen_stats.h
index 8cd8185..dcf5bfa 100644
--- a/include/net/gen_stats.h
+++ b/include/net/gen_stats.h
@@ -45,5 +45,6 @@
 extern int gen_replace_estimator(struct gnet_stats_basic *bstats,
 				 struct gnet_stats_rate_est *rate_est,
 				 spinlock_t *stats_lock, struct nlattr *opt);
+extern int gen_estimator_active(const struct gnet_stats_rate_est *rate_est);
 
 #endif