Add license to ndk_headers.

Test: make ndk
Bug: None
Change-Id: I02dae58dbc0762c538d81d1a48b2859ff4592aa9
diff --git a/Android.bp b/Android.bp
index 673843b..47e6f6b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -89,6 +89,7 @@
         "src/zlib.h",
         "src/zutil.h",
     ],
+    license: "NOTICE",
 }
 
 ndk_library {