Calculate IGMP checksum and use more reasonble max response time.

Also made IGMP properties configurable at runtime.

Change-Id: I98b40a43a0c17b7bf21f1bd622032c64d7434214
diff --git a/src/main/java/org/onosproject/cordmcast/CordMcast.java b/src/main/java/org/onosproject/cordmcast/CordMcast.java
index 86cd367..8fd533a 100644
--- a/src/main/java/org/onosproject/cordmcast/CordMcast.java
+++ b/src/main/java/org/onosproject/cordmcast/CordMcast.java
@@ -138,7 +138,9 @@
     private String fabricOnosUrl;
 
     @Activate
-    public void activate() {
+    public void activate(ComponentContext context) {
+        modified(context);
+
         appId = coreService.registerApplication("org.onosproject.cordmcast");
         componentConfigService.registerProperties(getClass());
         mcastService.addListener(listener);