Fix q_remove_tail

Previously, q_remove_tail always returned NULL without modifying
the list. Now, it properly removes the last element, copies its
value to the provided buffer, and returns the removed element.
This ensures correct queue behavior.

Change-Id: Ia4683122eebe47f7ac2fd55c1b57a12b33b1787f

Author: yy214123

queue.c

@@ -83,7 +83,14 @@ element_t *q_remove_head(struct list_head *head, char *sp, size_t bufsize)
 /* Remove an element from tail of queue */
 element_t *q_remove_tail(struct list_head *head, char *sp, size_t bufsize)
 {
-    return NULL;
+    if (!head || list_empty(head))
+        return NULL;
+    struct list_head *rm_node = head->prev;
+    element_t *rm_elem = list_entry(rm_node, element_t, list);
+    bufsize = strlen(rm_elem->value) + 1;
+    strlcpy(sp, rm_elem->value, bufsize);
+    list_del(rm_node);
+    return rm_elem;
 }
 
 /* Return number of elements in queue */