Android: Generate audio JNI code

This CL only affects the forked Android audio device code. The old code
at webrtc/modules/audio_device/android/ is unaffected.

Bug: webrtc:8689, webrtc:8278
Change-Id: I696b8297baba9a0f657ea3df808f57ebf259cb06
Reviewed-on: https://webrtc-review.googlesource.com/36502
Reviewed-by: Paulina Hensman <phensman@webrtc.org>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22528}

sdk/android/src/java/org/webrtc/CalledByNative.java

@@ -21,7 +21,7 @@ import java.lang.annotation.Target;
  */
 @Target({ElementType.CONSTRUCTOR, ElementType.METHOD})
 @Retention(RetentionPolicy.CLASS)
-@interface CalledByNative {
+public @interface CalledByNative {
   /*
    *  If present, tells which inner class the method belongs to.
    */