Add swapActiveStatsMap API for NetworkStatsFactory

This CL should be reverted before T sdk finalized.
This API is temporary added for the NetworkStatsFactory which is platform
code but will be moved into connectivity (tethering) mainline module.

Bug: 209935649
Test: atest CtsHostsideNetworkTests
Change-Id: I5894450f3089b2ea105722a18ddf8f1eed1c28a0

service/src/com/android/server/ConnectivityService.java

@@ -10660,4 +10660,14 @@ public class ConnectivityService extends IConnectivityManager.Stub
             throw new IllegalStateException(e);
         }
     }
+
+    @Override
+    public void swapActiveStatsMap() {
+        enforceNetworkStackOrSettingsPermission();
+        try {
+            mNetd.trafficSwapActiveStatsMap();
+        } catch (RemoteException | ServiceSpecificException e) {
+            throw new IllegalStateException(e);
+        }
+    }
 }