traced: add Android SDK level to system_info packet

This is necessary as on pre-release builds, we don't actually set a
version string and so we cannot parse the SDK version easily.

Change-Id: I3376c2a76a65b97407c4e7465781e7109f0e2d78
diff --git a/CHANGELOG b/CHANGELOG
index 7edf76f..40567f0 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,6 @@
 Unreleased:
   Tracing service and probes:
-    *
+    * Added Android SDK version to the SystemInfo trace packet.
   Trace Processor:
     *
   UI: