iwlwifi: Read outside array bounds

tid is bounded (above) by the size of default_tid_to_tx_fifo (17 elements), but
the size of priv->stations[].tid[] is MAX_TID_COUNT (9) elements.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-tx.c b/drivers/net/wireless/iwlwifi/iwl-tx.c
index 5febb31..2e89040 100644
--- a/drivers/net/wireless/iwlwifi/iwl-tx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-tx.c
@@ -1171,6 +1171,8 @@
 		IWL_ERR(priv, "Start AGG on invalid station\n");
 		return -ENXIO;
 	}
+	if (unlikely(tid >= MAX_TID_COUNT))
+		return -EINVAL;
 
 	if (priv->stations[sta_id].tid[tid].agg.state != IWL_AGG_OFF) {
 		IWL_ERR(priv, "Start AGG when state is not IWL_AGG_OFF !\n");