net: sched: make bstats per cpu and estimator RCU safe

In order to run qdisc's without locking statistics and estimators
need to be handled correctly.

To resolve bstats make the statistics per cpu. And because this is
only needed for qdiscs that are running without locks which is not
the case for most qdiscs in the near future only create percpu
stats when qdiscs set the TCQ_F_CPUSTATS flag.

Next because estimators use the bstats to calculate packets per
second and bytes per second the estimator code paths are updated
to use the per cpu statistics.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_generic.c

@@ -632,6 +632,9 @@ static void qdisc_rcu_free(struct rcu_head *head)
 {
 	struct Qdisc *qdisc = container_of(head, struct Qdisc, rcu_head);
 
+	if (qdisc_is_percpu_stats(qdisc))
+		free_percpu(qdisc->cpu_bstats);
+
 	kfree((char *) qdisc - qdisc->padded);
 }