pkt_sched: gen_kill_estimator() rcu fixes

gen_kill_estimator() API is incomplete or not well documented, since
caller should make sure an RCU grace period is respected before
freeing stats_lock.

This was partially addressed in commit 5d944c640b4
(gen_estimator: deadlock fix), but same problem exist for all
gen_kill_estimator() users, if lock they use is not already RCU
protected.

A code review shows xt_RATEEST.c, act_api.c, act_police.c have this
problem. Other are ok because they use qdisc lock, already RCU
protected.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/act_api.h b/include/net/act_api.h
index c05fd71..bab385f 100644
--- a/include/net/act_api.h
+++ b/include/net/act_api.h
@@ -20,6 +20,7 @@
 	struct gnet_stats_queue		tcfc_qstats;
 	struct gnet_stats_rate_est	tcfc_rate_est;
 	spinlock_t			tcfc_lock;
+	struct rcu_head			tcfc_rcu;
 };
 #define tcf_next	common.tcfc_next
 #define tcf_index	common.tcfc_index
@@ -32,6 +33,7 @@
 #define tcf_qstats	common.tcfc_qstats
 #define tcf_rate_est	common.tcfc_rate_est
 #define tcf_lock	common.tcfc_lock
+#define tcf_rcu		common.tcfc_rcu
 
 struct tcf_police {
 	struct tcf_common	common;