Add @Beta annotation because APIs is not stabilized yet

Change-Id: Id6111180be6c21a5287e2b53abacdfb43931abd4
diff --git a/core/api/src/main/java/org/onosproject/net/resource/device/IntentSetMultimap.java b/core/api/src/main/java/org/onosproject/net/resource/device/IntentSetMultimap.java
index 67c539d..f17bfb8 100644
--- a/core/api/src/main/java/org/onosproject/net/resource/device/IntentSetMultimap.java
+++ b/core/api/src/main/java/org/onosproject/net/resource/device/IntentSetMultimap.java
@@ -15,10 +15,12 @@
  */
 package org.onosproject.net.resource.device;
 
+import com.google.common.annotations.Beta;
 import org.onosproject.net.intent.IntentId;
 
 import java.util.Set;
 
+@Beta
 public interface IntentSetMultimap {
 
     /**