mac80211: make tx() operation return void

The return value of the tx operation is commonly
misused by drivers, leading to errors. All drivers
will drop frames if they fail to TX the frame, and
they must also properly manage the queues (if they
didn't, mac80211 would already warn).

Removing the ability for drivers to return a BUSY
value also allows significant cleanups of the TX
TX handling code in mac80211.

Note that this also fixes a bug in ath9k_htc, the
old "return -1" there was wrong.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Tested-by: Sedat Dilek <sedat.dilek@googlemail.com> [ath5k]
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com> [rt2x00]
Acked-by: Larry Finger <Larry.Finger@lwfinger.net> [b43, rtl8187, rtlwifi]
Acked-by: Luciano Coelho <coelho@ti.com> [wl12xx]
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/carl9170/tx.c

@@ -1339,7 +1339,7 @@ err_unlock_rcu:
 	return false;
 }
 
-int carl9170_op_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
+void carl9170_op_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
 {
 	struct ar9170 *ar = hw->priv;
 	struct ieee80211_tx_info *info;
@@ -1373,12 +1373,11 @@ int carl9170_op_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
 	}
 
 	carl9170_tx(ar);
-	return NETDEV_TX_OK;
+	return;
 
 err_free:
 	ar->tx_dropped++;
 	dev_kfree_skb_any(skb);
-	return NETDEV_TX_OK;
 }
 
 void carl9170_tx_scheduler(struct ar9170 *ar)