mac80211: add config tweak for tx bursting when using VHT

By default, set BE tx queue TXOP limit to 2.0 in the hostapd config
Many vendor drivers are doing similar things to boost throughput.
On MT7612 under ideal conditions, it improves tx throughput from 470 Mbit/s
to about 570 Mbit/s.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
(cherry-picked from commit 8650201f10afe83387fd6cde00b08172172eeba3)

package/kernel/mac80211/files/lib/netifd/wireless/mac80211.sh

@@ -23,6 +23,7 @@ drv_mac80211_init_device_config() {
 
 	config_add_string path phy 'macaddr:macaddr'
 	config_add_string hwmode
+	config_add_string tx_burst
 	config_add_int beacon_int chanbw frag rts
 	config_add_int rxantenna txantenna antenna_gain txpower distance
 	config_add_boolean noscan ht_coex
@@ -97,9 +98,10 @@ mac80211_hostapd_setup_base() {
 	[ "$auto_channel" -gt 0 ] && json_get_values channel_list channels
 
 	json_get_vars noscan ht_coex
-	json_get_values ht_capab_list ht_capab
+	json_get_values ht_capab_list ht_capab tx_burst
 
 	[ -n "$noscan" -a "$noscan" -gt 0 ] && hostapd_noscan=1
+	[ "$tx_burst" = 0 ] && tx_burst=
 
 	ieee80211n=1
 	ht_capab=
@@ -229,6 +231,7 @@ mac80211_hostapd_setup_base() {
 			vht_link_adapt:3 \
 			vht160:2
 
+		set_default tx_burst 2.0
 		append base_cfg "ieee80211ac=1" "$N"
 		vht_cap=0
 		for cap in $(iw phy "$phy" info | awk -F "[()]" '/VHT Capabilities/ { print $2 }'); do
@@ -310,6 +313,7 @@ mac80211_hostapd_setup_base() {
 ${channel:+channel=$channel}
 ${channel_list:+chanlist=$channel_list}
 ${hostapd_noscan:+noscan=1}
+${tx_burst:+tx_queue_data2_burst=$tx_burst}
 $base_cfg
 
 EOF