[MINOR] add LIST_HEAD_INIT to the list management macros

It is useful to have the ability to initialize a list while declaring it.
diff --git a/include/common/mini-clist.h b/include/common/mini-clist.h
index a2a86bd..caed2dc 100644
--- a/include/common/mini-clist.h
+++ b/include/common/mini-clist.h
@@ -23,6 +23,8 @@
 
 #define LIST_INIT(l) ((l)->n = (l)->p = (l))
 
+#define LIST_HEAD_INIT(l) { &l, &l }
+
 /* dual linked lists :
  * Start = (struct list *) pointer to the next elem's prev list entry
  * For each element :