FlowId's valueOf should be static.

Change-Id: I585c1e2ea2eba48b9fac92117354495f0d7b2e8a
diff --git a/core/api/src/main/java/org/onlab/onos/net/flow/FlowId.java b/core/api/src/main/java/org/onlab/onos/net/flow/FlowId.java
index d4e32a8..03140f7 100644
--- a/core/api/src/main/java/org/onlab/onos/net/flow/FlowId.java
+++ b/core/api/src/main/java/org/onlab/onos/net/flow/FlowId.java
@@ -11,7 +11,7 @@
         this.flowid = id;
     }
 
-    public FlowId valueOf(int id) {
+    public static FlowId valueOf(int id) {
         return new FlowId(id);
     }