iwlwifi: mvm: Allow retries for probe responses

When hostapd sends a probe response, it does not request an
acknowledgment on the probe response. This setting is propagated
to the driver and FW from mac80211, and as a result probe responses
are transmitted only once without retries. In congested
environments, this reduces the likelihood for finding the AP.

To overcome this, enable acknowledgment and retries for probe
responses, even in case no acknowledgment is requested. In such
a case the retry limit is set to 3.
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

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

@@ -209,7 +209,9 @@ void iwl_mvm_set_tx_cmd(struct iwl_mvm *mvm, struct sk_buff *skb,
 	u16 offload_assist = 0;
 	u8 ac;
 
-	if (!(info->flags & IEEE80211_TX_CTL_NO_ACK))
+	if (!(info->flags & IEEE80211_TX_CTL_NO_ACK) ||
+	    (ieee80211_is_probe_resp(fc) &&
+	     !is_multicast_ether_addr(hdr->addr1)))
 		tx_flags |= TX_CMD_FLG_ACK;
 	else
 		tx_flags &= ~TX_CMD_FLG_ACK;