fix generation of legacy type maps for message superclasses

My commit 4db4d043 changed the contents of the message_types dictionary to
include all message classes, including subclasses of stats and flow mods. The
old handcoded type maps did not include the subclasses. The change caused the
generated C of_message_type_to_id tables to be incorrect.

This change removes the subclasses from the generated message_types dictionary.
add check-c make target

This makes it easier to run locitest.