Enable checkstyle rule for static variable names.

Enable the checkstyle rule that checks the names of
static variables and fix any violations that
are detected.

Change-Id: I2918a85b13b343285da99223829187a87ad280c3
diff --git a/src/main/java/net/onrc/onos/core/devicemanager/OnosDevice.java b/src/main/java/net/onrc/onos/core/devicemanager/OnosDevice.java
index f5a405d..157d52f 100644
--- a/src/main/java/net/onrc/onos/core/devicemanager/OnosDevice.java
+++ b/src/main/java/net/onrc/onos/core/devicemanager/OnosDevice.java
@@ -38,7 +38,7 @@
  */
 public class OnosDevice implements Serializable { //implements Comparable<OnosDevice> {
 
-    private static int ACTIVITY_TIMEOUT = 30000;
+    private static final int ACTIVITY_TIMEOUT = 30000;
 
     /**
      * The MAC address associated with this entity.