Fix: make vndk namespace visible for 2016 Pixes

The nativeloader tries to find the 'vndk' namespace when there is a
vendor apk in the classloader paths. This can happen even for a
downloaded app if the app is using a vendor apk via <uses-library> tag.

In order to prevent the nativeloader from failing to find the vndk
namespace, the namespace is marked as visible.

Bug: 66482442
Test: download the app mentioned in the bug, it does not crash.
Change-Id: I82e2394eb6eedcb8645e1a5b3735bbfe2735b312