Allow LinkCollectionIntent to accept other types of resources.

Change-Id: I54331506a8e58efa7235da86e604d174fd5a72ec
diff --git a/core/api/src/main/java/org/onosproject/net/intent/ConnectivityIntent.java b/core/api/src/main/java/org/onosproject/net/intent/ConnectivityIntent.java
index 6febfab..113845d 100644
--- a/core/api/src/main/java/org/onosproject/net/intent/ConnectivityIntent.java
+++ b/core/api/src/main/java/org/onosproject/net/intent/ConnectivityIntent.java
@@ -29,7 +29,7 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
-
+import static com.google.common.base.MoreObjects.firstNonNull;
 import static com.google.common.base.Preconditions.checkNotNull;
 
 /**
@@ -195,6 +195,21 @@
     /**
      * Produces a collection of network resources from the given links.
      *
+     * @param resources base resources
+     * @param links collection of links
+     * @return collection of resources
+     */
+    protected static Collection<NetworkResource> resources(Collection<NetworkResource> resources,
+                                                           Collection<Link> links) {
+        return ImmutableSet.<NetworkResource>builder()
+                .addAll(firstNonNull(resources, ImmutableList.of()))
+                .addAll(links)
+                .build();
+    }
+
+    /**
+     * Produces a collection of network resources from the given links.
+     *
      * @param links collection of links
      * @return collection of link resources
      */