ONOS-2294: Redefine LinkResource as interface

LinkResource was defined as an abstract class, but it doesn't define any
methods. Maker interface fits this case.

Note: This change may break backward compatibility for those defining a
sub-class of LinkResource.

Change-Id: I53cb7e8eae7057d07c63960c488979a99cd54d52

@@ -24,7 +24,7 @@ import static com.google.common.base.Preconditions.checkNotNull;
 /**
  * Representation of bandwidth resource in bps.
  */
-public final class BandwidthResource extends LinkResource {
+public final class BandwidthResource implements LinkResource {
 
     private final Bandwidth bandwidth;
 

@@ -24,7 +24,7 @@ import static com.google.common.base.Preconditions.checkNotNull;
 /**
  * Representation of lambda resource.
  */
-public final class LambdaResource extends LinkResource {
+public final class LambdaResource implements LinkResource {
 
     private final IndexedLambda lambda;
 

@@ -18,6 +18,5 @@ package org.onosproject.net.resource.link;
 /**
  * Abstraction of link resource.
  */
-public abstract class LinkResource {
-
+public interface LinkResource {
 }

@@ -21,7 +21,7 @@ import java.util.Objects;
 /**
  * Representation of MPLS label resource.
  */
-public final class MplsLabel extends LinkResource {
+public final class MplsLabel implements LinkResource {
 
     private final org.onlab.packet.MplsLabel mplsLabel;