Fix small bug in pre-written OFGroup.java. Replace MAX with ZERO.
diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/OFGroup.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/OFGroup.java
index 32e9bcc..d9981d4 100644
--- a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/OFGroup.java
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/OFGroup.java
@@ -62,7 +62,7 @@
     public static OFGroup of(final int groupNumber) {
         switch(groupNumber) {
             case ZERO_VAL:
-                return MAX;
+                return ZERO;
             case MAX_VAL:
                 return MAX;
             case ALL_VAL: