Fix q_remove_head

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

Change-Id: I32dd35453dac36972dce69c825703125bb54b27d

Author: yy214123

queue.c

@@ -70,7 +70,14 @@ bool q_insert_tail(struct list_head *head, char *s)
 /* Remove an element from head of queue */
 element_t *q_remove_head(struct list_head *head, char *sp, size_t bufsize)
 {
-    return NULL;
+    if (!head || list_empty(head))
+        return NULL;
+    struct list_head *rm_node = head->next;
+    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;
 }
 
 /* Remove an element from tail of queue */