iwlwifi: add IEEE80211_AMPDU_TX_OPERATIONAL

mac80211 do not check the return code now, what if mac80211 does start
using the return code? IEEE80211_AMPDU_TX_OPERATIONAL is a valid action,
just iwlwifi driver do not need to take any action for it; so instead of
return "-EINVAL", it is a good program practice to return "-EOPNOTSUPP"
to make sure mac80211 will not get wrong impression.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-agn.c

@@ -2955,6 +2955,9 @@ static int iwl_mac_ampdu_action(struct ieee80211_hw *hw,
 			return 0;
 		else
 			return ret;
+	case IEEE80211_AMPDU_TX_OPERATIONAL:
+		/* do nothing */
+		return -EOPNOTSUPP;
 	default:
 		IWL_DEBUG_HT(priv, "unknown\n");
 		return -EINVAL;