quality: Add test cases for group_desc and group_features messages

lib/openflow/multipart/group_desc/request.ex

@@ -4,11 +4,20 @@ defmodule Openflow.Multipart.GroupDesc.Request do
     xid: 0,
     # virtual field
     datapath_id: nil,
+    aux_id: nil,
     flags: []
   )
 
   alias __MODULE__
 
+  @type t :: %Request{
+          version: 4,
+          datapath_id: String.t(),
+          aux_id: 0..0xFF | nil,
+          xid: 0..0xFFFFFFFF,
+          flags: [:more]
+        }
+
   def ofp_type, do: 18
 
   def new(xid \\ 0) do