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/EcmpShortestPathGraph.java b/src/main/java/org/onosproject/segmentrouting/EcmpShortestPathGraph.java
index 202a564..49bf80f 100644
--- a/src/main/java/org/onosproject/segmentrouting/EcmpShortestPathGraph.java
+++ b/src/main/java/org/onosproject/segmentrouting/EcmpShortestPathGraph.java
@@ -74,7 +74,7 @@
             currDistance = distanceQueue.poll();
 
             for (Link link : srManager.linkService.getDeviceEgressLinks(sw)) {
-                if (srManager.avoidLink(link)) {
+                if (srManager.linkHandler.avoidLink(link)) {
                     continue;
                 }
                 DeviceId reachedDevice = link.dst().deviceId();