Implement q_size function

The q_size function returns the number of nodes in the queue.

Change-Id: I4fc028ef627bff46f84e77bbf042b3e51a6f02e4

Author: JeepWay

queue.c

@@ -117,7 +117,16 @@ element_t *q_remove_tail(struct list_head *head, char *sp, size_t bufsize)
 /* Return number of elements in queue */
 int q_size(struct list_head *head)
 {
-    return -1;
+    if (!head)
+        return 0;
+
+    int size = 0;
+    struct list_head *node;
+
+    list_for_each (node, head)
+        size++;
+
+    return size;
 }
 
 /* Delete the middle node in queue */