perfetto: Turning off system prop should stop service

Test: manual
Change-Id: Ie8128212a2a595f7b1e7cbb6ef256305c3446967
diff --git a/perfetto.rc b/perfetto.rc
index 82332f9..c384406 100644
--- a/perfetto.rc
+++ b/perfetto.rc
@@ -39,3 +39,7 @@
 
     start traced
     start traced_probes
+
+on property:persist.traced.enable=0
+    stop traced
+    stop traced_probes