Address comments in gerrit 20328

Create a new class XconnecEndpoint to cover both physical port and load balancer
Also change the CLI load balancer identifier to "LB:"

Change-Id: I0b4cd6e474d8b21468d87fcadd9280fdf7d6aafa
diff --git a/app/src/main/java/org/onosproject/segmentrouting/xconnect/api/XconnectService.java b/app/src/main/java/org/onosproject/segmentrouting/xconnect/api/XconnectService.java
index fe51b06..2fe6488 100644
--- a/app/src/main/java/org/onosproject/segmentrouting/xconnect/api/XconnectService.java
+++ b/app/src/main/java/org/onosproject/segmentrouting/xconnect/api/XconnectService.java
@@ -44,9 +44,9 @@
      *
      * @param deviceId device ID
      * @param vlanId VLAN ID
-     * @param ports set of ports
+     * @param endpoints set of endpoints
      */
-    void addOrUpdateXconnect(DeviceId deviceId, VlanId vlanId, Set<String> ports);
+    void addOrUpdateXconnect(DeviceId deviceId, VlanId vlanId, Set<XconnectEndpoint> endpoints);
 
     /**
      * Deletes Xconnect.