MINOR: lists: Implement function to convert list => mt_list and mt_list => list

Implement mt_list_to_list() and list_to_mt_list(), to be able to convert
from a struct list to a struct mt_list, and vice versa.
This is normally of no use, except for struct connection's list field, that
can go in either a struct list or a struct mt_list.
diff --git a/include/common/mini-clist.h b/include/common/mini-clist.h
index a7b5a5d..40baf5d 100644
--- a/include/common/mini-clist.h
+++ b/include/common/mini-clist.h
@@ -662,4 +662,28 @@
 			}                                                     \
 	    }),                                                               \
 	     &item->member != (list_head);)
+
+static __inline struct list *mt_list_to_list(struct mt_list *list)
+{
+	union {
+		struct mt_list *mt_list;
+		struct list *list;
+	} mylist;
+
+	mylist.mt_list = list;
+	return mylist.list;
+}
+
+static __inline struct mt_list *list_to_mt_list(struct list *list)
+{
+		union {
+		struct mt_list *mt_list;
+		struct list *list;
+	} mylist;
+
+	mylist.list = list;
+	return mylist.mt_list;
+
+}
+
 #endif /* _COMMON_MINI_CLIST_H */