Make ResourceService API more flexible in parameter

Change-Id: Ic8b803cc6ae3b2798de525bfd6545ac5c57e8fdd
diff --git a/core/api/src/main/java/org/onosproject/net/resource/ResourceService.java b/core/api/src/main/java/org/onosproject/net/resource/ResourceService.java
index b52b6b9..7a75296 100644
--- a/core/api/src/main/java/org/onosproject/net/resource/ResourceService.java
+++ b/core/api/src/main/java/org/onosproject/net/resource/ResourceService.java
@@ -64,7 +64,7 @@
      * @param resources resources to be allocated
      * @return non-empty list of allocation information if succeeded, otherwise empty list
      */
-    List<ResourceAllocation> allocate(ResourceConsumer consumer, List<Resource> resources);
+    List<ResourceAllocation> allocate(ResourceConsumer consumer, List<? extends Resource> resources);
 
     /**
      * Transactionally allocates the specified resources to the specified user.