Implement q_insert_head & q_insert_tail

This commit implements the function to allocate a new element
into the head or tail of the list.
Using list_add & list_add_tail to implement this two funtions.
If allocated FAILED, it will free the new element and return
false to avoid memory leak.

Change-Id: I10544fc8019a7d7e6b1fd52d8dd4588e486c1740

Author: Mike1117

queue.c

@@ -36,12 +36,30 @@ void q_free(struct list_head *head)
 /* Insert an element at head of queue */
 bool q_insert_head(struct list_head *head, char *s)
 {
+    if (!head || !s)
+        return false;
+    element_t *node = malloc(sizeof(element_t));
+    node->value = strdup(s);
+    if (!node->value) {
+        free(node);
+        return false;
+    }
+    list_add(&node->list, head);
     return true;
 }
 
 /* Insert an element at tail of queue */
 bool q_insert_tail(struct list_head *head, char *s)
 {
+    if (!head || !s)
+        return false;
+    element_t *node = malloc(sizeof(element_t));
+    node->value = strdup(s);
+    if (!node->value) {
+        free(node);
+        return false;
+    }
+    list_add_tail(&node->list, head);
     return true;
 }