MINOR: lua: use the hlua_rule type in place of opaque type

The (http|tcp)-(request|response) action rules use common
opaque type. For the HAProxy embbedded feature, types are know,
it better to add this types in the action union and use it.
diff --git a/include/types/action.h b/include/types/action.h
index 3333fb0..1cb4aa9 100644
--- a/include/types/action.h
+++ b/include/types/action.h
@@ -56,6 +56,7 @@
 			struct list key;       /* pattern to retrieve MAP or ACL key */
 			struct list value;     /* pattern to retrieve MAP value */
 		} map;
+		struct hlua_rule *hlua_rule;
 		struct {
 			void *p[4];
 		} act;                         /* generic pointers to be used by custom actions */
diff --git a/include/types/hlua.h b/include/types/hlua.h
index 357f7ab..f481bdf 100644
--- a/include/types/hlua.h
+++ b/include/types/hlua.h
@@ -123,6 +123,7 @@
 /* Empty struct for compilation compatibility */
 struct hlua { };
 struct hlua_socket { };
+struct hlua_rule { };
 
 #endif /* USE_LUA */