GUI -- Fixed a defect where showTraffic was sending redundant link classes.

Change-Id: I7fd1385cc6e200f1b61930e218cc82041084e0a7

@@ -656,7 +656,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
         Map<String, ObjectNode> pathNodes = new HashMap<>();
         for (BiLink biLink : biLinks.values()) {
             boolean hasTraffic = biLink.hasTraffic;
-            String tc = (biLink.classes + (hasTraffic ? " animated" : "")).trim();
+            String tc = (biLink.classes() + (hasTraffic ? " animated" : "")).trim();
             ObjectNode pathNode = pathNodes.get(tc);
             if (pathNode == null) {
                 pathNode = mapper.createObjectNode()
@@ -830,7 +830,8 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
         public Link two;
         public boolean hasTraffic = false;
         public long bytes = 0;
-        public String classes = "";
+
+        private Set<String> classes = new HashSet<>();
 
         BiLink(LinkKey key, Link link) {
             this.key = key;
@@ -849,7 +850,13 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
         }
 
         void addClass(String trafficClass) {
-            classes = classes + " " + trafficClass;
+            classes.add(trafficClass);
+        }
+
+        String classes() {
+            StringBuilder sb = new StringBuilder();
+            classes.forEach(c -> sb.append(c).append(" "));
+            return sb.toString().trim();
         }
     }