Take down edge ports on a leaf switch when all uplinks are gone

- Bug fix for case when all uplinks are gone, but dual-homed host continues to send packets to switch;
  We now administratively take down the host port to force the host to use the other leaf in the pair.
- Restructured SR manager by creating a LinkHandler
- fixed/added some log messages

Change-Id: I3722cd364dc8798b16891519bec165627e92bd87
diff --git a/src/main/java/org/onosproject/segmentrouting/SegmentRoutingNeighbourDispatcher.java b/src/main/java/org/onosproject/segmentrouting/SegmentRoutingNeighbourDispatcher.java
index cc815da..f170fae 100644
--- a/src/main/java/org/onosproject/segmentrouting/SegmentRoutingNeighbourDispatcher.java
+++ b/src/main/java/org/onosproject/segmentrouting/SegmentRoutingNeighbourDispatcher.java
@@ -42,7 +42,8 @@
 
     @Override
     public void handleMessage(NeighbourMessageContext context, HostService hostService) {
-        log.trace("Received a {} packet {}", context.protocol(), context.packet());
+        log.trace("Received {} packet on {}: {}", context.protocol(),
+                  context.inPort(), context.packet());
         switch (context.protocol()) {
             case ARP:
                 if (this.manager.arpHandler != null) {