Unversion NDK stub libraries.

The system versions of these libraries aren't versioned yet.

Bug: https://github.com/android-ndk/ndk/issues/278
Test: make ndk
Change-Id: I1aa674433bea241dfd863a0382df6d59d067f282
diff --git a/media/liboboe/Android.bp b/media/liboboe/Android.bp
index 0d22e65..bfcc049 100644
--- a/media/liboboe/Android.bp
+++ b/media/liboboe/Android.bp
@@ -24,4 +24,5 @@
     name: "liboboe.ndk",
     symbol_file: "liboboe.map.txt",
     first_version: "26",
+    unversioned_until: "current",
 }