Fixed some PMD issues in the SDN-IP module

Change-Id: Iaf002e70c1a00f0008edef5e77b91579acf146aa
diff --git a/src/main/java/net/onrc/onos/apps/bgproute/PushedFlowMod.java b/src/main/java/net/onrc/onos/apps/bgproute/PushedFlowMod.java
index 612a704..fc13cd3 100644
--- a/src/main/java/net/onrc/onos/apps/bgproute/PushedFlowMod.java
+++ b/src/main/java/net/onrc/onos/apps/bgproute/PushedFlowMod.java
@@ -9,7 +9,7 @@
  * TODO This functionality should be handled by ONOS's flow layer in future.
  */
 public class PushedFlowMod {
-    private long dpid;
+    private final long dpid;
     private OFFlowMod flowMod;
 
     public PushedFlowMod(long dpid, OFFlowMod flowMod) {