iwlwifi: iwl_mvm_tx_mpdu() must be called with BH disabled

As iwl_mvm_tx_mpdu() is not disabling BH while obtaining iwl_mvm_sta->lock
(which is being taken from BH context as well), it has to be always
invoked with BH disabled. Make that clear in a comment.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/tx.c

@@ -1063,7 +1063,9 @@ static int iwl_mvm_tx_pkt_queued(struct iwl_mvm *mvm,
 }
 
 /*
- * Sets the fields in the Tx cmd that are crypto related
+ * Sets the fields in the Tx cmd that are crypto related.
+ *
+ * This function must be called with BHs disabled.
  */
 static int iwl_mvm_tx_mpdu(struct iwl_mvm *mvm, struct sk_buff *skb,
 			   struct ieee80211_tx_info *info,