loci: store unmangled class name in inheritance_map

Instead of just the portion after the base class name.
diff --git a/c_gen/loxi_utils_legacy.py b/c_gen/loxi_utils_legacy.py
index 5d6d1d9..2f5e672 100644
--- a/c_gen/loxi_utils_legacy.py
+++ b/c_gen/loxi_utils_legacy.py
@@ -219,6 +219,10 @@
     """
     return parent + "_" + instance
 
+def class_to_instance(cls, base_cls):
+    assert cls.startswith(base_cls + '_')
+    return cls[len(base_cls)+1:]
+
 def class_is_var_len(cls, version):
     # Match is special case.  Only version 1.2 (wire version 3) is var
     if cls == "of_match":