Raise API level to 23.

Now apps can target both MNC and 23.

Change-Id: Ife6a844dc1a12b5d37973cbb890434c950dab7aa
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 4a87abb..e384526 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -53,7 +53,7 @@
   # intermediate builds).  During development, this number remains at the
   # SDK version the branch is based on and PLATFORM_VERSION_CODENAME holds
   # the code-name of the new development work.
-  PLATFORM_SDK_VERSION := 22
+  PLATFORM_SDK_VERSION := 23
 endif
 
 ifeq "" "$(PLATFORM_VERSION_CODENAME)"