hash: add hash_list_idx() (#427)

Useful for manual hash list iteration.

include/re_hash.h

@@ -15,6 +15,7 @@ void hash_unlink(struct le *le);
 struct le *hash_lookup(const struct hash *h, uint32_t key, list_apply_h *ah,
 		       void *arg);
 struct le *hash_apply(const struct hash *h, list_apply_h *ah, void *arg);
+struct list *hash_list_idx(const struct hash *h, uint32_t i);
 struct list *hash_list(const struct hash *h, uint32_t key);
 uint32_t hash_bsize(const struct hash *h);
 void hash_flush(struct hash *h);

src/hash/hash.c

@@ -140,7 +140,24 @@ struct le *hash_apply(const struct hash *h, list_apply_h *ah, void *arg)
 
 
 /**
- * Return bucket list for a given index
+ * Return bucket list for a given bucket index
+ *
+ * @param h  Hashmap table
+ * @param i  Bucket index
+ *
+ * @return Bucket list if valid input, otherwise NULL
+ */
+struct list *hash_list_idx(const struct hash *h, uint32_t i)
+{
+	if (!h || i >= h->bsize)
+		return NULL;
+
+	return &h->bucket[i];
+}
+
+
+/**
+ * Return bucket list for a given key
  *
  * @param h   Hashmap table
  * @param key Hash key