reset device ap's blocking algorithm computation on topology change.

src/main/java/net/floodlightcontroller/devicemanager/DeviceAttachmentPoint.java

@@ -46,8 +46,7 @@ public class DeviceAttachmentPoint {
         this.lastSeenInStorage = null;
         this.lastWrittenToStorage = null;
         
-        this.lastConflict = null;
-        this.conflictFrequency = 0;
+        resetConflictState();
     }
     
     public SwitchPortTuple getSwitchPort() {
@@ -138,6 +137,12 @@ public class DeviceAttachmentPoint {
         conflictFrequency += 100;
     }
     
+    public void resetConflictState() {
+        lastConflict = null;
+        conflictFrequency = 0;
+        setBlocked(false);
+    }
+    
     public boolean isInConflict() {
         return lastConflict != null;
     }

src/main/java/net/floodlightcontroller/devicemanager/internal/DeviceManagerImpl.java

@@ -1670,11 +1670,11 @@ public class DeviceManagerImpl implements IDeviceManagerService, IOFMessageListe
              * Also make sure the attachmentPoints are in non-blocked state
              */
             for (DeviceAttachmentPoint dap: tempAPMap.values()) {
-                dap.setBlocked(false);
+            	dap.resetConflictState();
             }
             d.setAttachmentPoints(tempAPMap.values());
             for (DeviceAttachmentPoint dap : tempOldAPMap.values()) {
-                dap.setBlocked(false);
+                dap.resetConflictState();
                 d.addOldAttachmentPoint(dap);
             }