wil6210: handle tx completions only if vring tx data is enabled

wil_vring_fini_tx is called in disconnect in order to free the
allocated vrings.
wil_vring_fini_tx is disabling the vring_tx_data before napi_synchronize
is called in order to avoid the tx handling of this vring, while
wil_vring_free is called only after napi finished the current handling
of the tx completed packets.
Due to that, in case of disconnect, wil6210_netdev_poll_tx can be called
when vring->va is not NULL but vring_tx_data[i]->enabled is already
disabled.

This patch checks vring_tx_data[i]->enabled in wil6210_netdev_poll_tx
to prevent handling of disabled vrings.
Signed-off-by: NMaya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: NKalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/wil6210/netdev.c

 /*
- * Copyright (c) 2012-2015 Qualcomm Atheros, Inc.
+ * Copyright (c) 2012-2016 Qualcomm Atheros, Inc.
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -108,8 +108,9 @@ static int wil6210_netdev_poll_tx(struct napi_struct *napi, int budget)
 	/* always process ALL Tx complete, regardless budget - it is fast */
 	for (i = 0; i < WIL6210_MAX_TX_RINGS; i++) {
 		struct vring *vring = &wil->vring_tx[i];
+		struct vring_tx_data *txdata = &wil->vring_tx_data[i];
 
-		if (!vring->va)
+		if (!vring->va || !txdata->enabled)
 			continue;
 
 		tx_done += wil_tx_complete(wil, i);