Combine per-error-type error code enums into a single error code enum

- also suppress code generation of OFPortNo which is already handled
  by the pre-written OFPort class
diff --git a/java_gen/codegen.py b/java_gen/codegen.py
index b84556c..d94d78a 100644
--- a/java_gen/codegen.py
+++ b/java_gen/codegen.py
@@ -50,7 +50,7 @@
         shutil.rmtree(basedir)
     os.makedirs(basedir)
     copy_prewrite_tree(basedir)
-
+    java_model.adjust_ir()
     gen = JavaGenerator(basedir)
     gen.create_of_interfaces()
     gen.create_of_classes()