manifest: update to r24

Change-Id: Ic47840f031404c657bfadba5c8012f38c52ebe99
diff --git a/default.xml b/default.xml
index 8031700..b6a1603 100644
--- a/default.xml
+++ b/default.xml
@@ -21,7 +21,7 @@
   <remote  name="private"
            fetch="ssh://git@github.com" />
 
-  <default revision="refs/tags/android-6.0.1_r22"
+  <default revision="refs/tags/android-6.0.1_r24"
            remote="aosp"
            sync-j="4" />