Fix the doc of addCrossProfileIntentFilter.

Mention that cross-profile-intent-filters only work for activity intents.

BUG:18776618

Change-Id: I209d1e38641b4ae84b682a2525e6ddae603a71f9

core/java/android/app/admin/DevicePolicyManager.java

@@ -2781,6 +2781,8 @@ public class DevicePolicyManager {
     /**
      * Called by the profile owner of a managed profile so that some intents sent in the managed
      * profile can also be resolved in the parent, or vice versa.
+     * Only activity intents are supported.
+     *
      * @param admin Which {@link DeviceAdminReceiver} this request is associated with.
      * @param filter The {@link IntentFilter} the intent has to match to be also resolved in the
      * other profile