Fix VolumeShaper unducking for OpenSLES playback

Native PlayerBase::applyVolumeShaper was never called (silent failure)
due to an undeclared nullable InterpolatorConfig parcelable
which was sent as null.

Test: see bug for repro details
Bug: 185372526
Change-Id: Id18664978605602f287e15de0c920ffc83a9aada
diff --git a/aidl/android/media/VolumeShaperConfiguration.aidl b/aidl/android/media/VolumeShaperConfiguration.aidl
index 6361851..824c169 100644
--- a/aidl/android/media/VolumeShaperConfiguration.aidl
+++ b/aidl/android/media/VolumeShaperConfiguration.aidl
@@ -29,5 +29,5 @@
     /** Bitmask, indexed by VolumeShaperConfigurationOptionFlag. */
     int optionFlags;
     double durationMs;
-    InterpolatorConfig interpolatorConfig;
+    @nullable InterpolatorConfig interpolatorConfig; // null if type == ID
 }