iwlwifi: don't modify the timer if we don't Tx

In fragmentation we don't update the write pointer of the
HW immediately. So we shouldn't modify the timer in that
case.
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/iwlwifi/pcie/trans.c

@@ -1354,7 +1354,8 @@ static int iwl_trans_pcie_tx(struct iwl_trans *trans, struct sk_buff *skb,
 			     skb->data + hdr_len, secondlen);
 
 	/* start timer if queue currently empty */
-	if (q->read_ptr == q->write_ptr && trans_pcie->wd_timeout)
+	if (txq->need_update && q->read_ptr == q->write_ptr &&
+	    trans_pcie->wd_timeout)
 		mod_timer(&txq->stuck_timer, jiffies + trans_pcie->wd_timeout);
 
 	/* Tell device the write index *just past* this latest filled TFD */