Mark the module as VNDK or VNDK-SP in Android.bp

As a VNDK/VNDK-SP module, Android.bp must have 'vndk' tag as well
as 'vendor_available: true'.

For a VNDK module, the 'vndk' tag has 'enabled: true'.
It will be installed system/lib(64)/vndk as a vendor variant.

For a VNDK-SP module, the 'vndk' tag has
'support_system_process: true' as well as 'enabled: true'.
It will be installed system/lib(64)/vndk-sp as a vendor variant.

Bug: 63866913
Test: build and boot with BOARD_VNDK_VERSION=current
Change-Id: I50f7d1df4ed1ea1928d0881495e28ae4f379acf5
diff --git a/Android.bp b/Android.bp
index 53828f6..f7b0a10 100644
--- a/Android.bp
+++ b/Android.bp
@@ -2,6 +2,9 @@
 cc_library {
     name: "libnl",
     vendor_available: true,
+    vndk: {
+        enabled: true,
+    },
 
     srcs: [
         "lib/cache.c",