Add test command for disabling/enabling A-MPDU aggregation

ctrl_iface command "SET ampdu <0/1>" can now be used to
disable/enable A-MPDU aggregation.

src/drivers/driver_ndis.c

@@ -3307,5 +3307,6 @@ const struct wpa_driver_ops wpa_driver_ndis_ops = {
 	NULL /* shared_freq */,
 	NULL /* get_noa */,
 	NULL /* set_noa */,
-	NULL /* set_p2p_powersave */
+	NULL /* set_p2p_powersave */,
+	NULL /* ampdu */
 };