Mention that setMasterVolumeMuted has no effect when set on a managed profile.

BUG:27262893
Change-Id: Ibbcf4f222e47e9e0b723ec4b0335f100e904bca1
diff --git a/core/java/android/app/admin/DevicePolicyManager.java b/core/java/android/app/admin/DevicePolicyManager.java
index 540678e..a207a52 100644
--- a/core/java/android/app/admin/DevicePolicyManager.java
+++ b/core/java/android/app/admin/DevicePolicyManager.java
@@ -5498,6 +5498,7 @@
 
     /**
      * Called by profile or device owners to set the master volume mute on or off.
+     * This has no effect when set on a managed profile.
      *
      * @param admin Which {@link DeviceAdminReceiver} this request is associated with.
      * @param on {@code true} to mute master volume, {@code false} to turn mute off.