Add product_available to product available modules

vendor_available modules were available to product modules.
However, not all vendor_available modules are required to be
available to product modules. Some modules want to be available only
to product modules but not vendor modules.

To cover the requirement, we separate product_available from
vendor_available.
vendor_available will not provide product available module.

Bug: 150902910
Test: build
Change-Id: I2ffd02cf8cc08fbe40f3d06ec071aad86d09740e
diff --git a/Android.bp b/Android.bp
index 58122ef..6ad995a 100644
--- a/Android.bp
+++ b/Android.bp
@@ -3,6 +3,7 @@
     name: "libnl",
     host_supported: true,
     vendor_available: true,
+    product_available: true,
     vndk: {
         enabled: true,
     },