tc: check for errors in gen_rate_estimator creation

The functions gen_new_estimator and gen_replace_estimator can return
errors, but they were being ignored.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 3fcfd4e..f859dd5 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -880,9 +880,12 @@
 	sch->stab = stab;
 
 	if (tca[TCA_RATE])
+		/* NB: ignores errors from replace_estimator
+		   because change can't be undone. */
 		gen_replace_estimator(&sch->bstats, &sch->rate_est,
-				      qdisc_root_sleeping_lock(sch),
-				      tca[TCA_RATE]);
+					    qdisc_root_sleeping_lock(sch),
+					    tca[TCA_RATE]);
+
 	return 0;
 }