Revert "Temporary disable rate-limit cache for TrafficStats"

This reverts commit 21b36d8c6856849c491578e8b86909b2475e2de7.

Reason for revert: Re-enable feature with test fixes

Change-Id: I370e93fe0ff550fe8199e1502e5a0af219de38e5
diff --git a/service-t/src/com/android/server/net/NetworkStatsService.java b/service-t/src/com/android/server/net/NetworkStatsService.java
index 8305c1e..d43c3da 100644
--- a/service-t/src/com/android/server/net/NetworkStatsService.java
+++ b/service-t/src/com/android/server/net/NetworkStatsService.java
@@ -926,7 +926,8 @@
          * to ensure that the code does not need to deal with flag values changing at runtime.
          */
         public boolean supportTrafficStatsRateLimitCache(@NonNull Context ctx) {
-            return false;
+            return SdkLevel.isAtLeastV() && DeviceConfigUtils.isTetheringFeatureNotChickenedOut(
+                    ctx, TRAFFICSTATS_RATE_LIMIT_CACHE_ENABLED_FLAG);
         }
 
         /**