[FS#896] mt7620 - dropping frames (WiFi)

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - A (drut) 

Attached to Project - LEDE Project
Summary - mt7620 - dropping frames (WiFi)
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - High
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - Device: Nexx WT3020 (MT7620)
LEDE release: LEDE Reboot 17.01-SNAPSHOT r3435-65eec8b

Latest LEDE on Nexx WT3020 with MT7620 is getting syslog spammed with:
ieee80211 phy0: rt2x00queue_write_tx_frame: Error - Dropping frame due to full tx queue 2

It usually occurs with high-bandwidth usage of WiFi client (Android i.e.) and results with need to reboot router (or WiFi won't even work for devices - it's seen but unable to connect).

# cat /etc/config/wireless

config wifi-device 'radio0'
        option type 'mac80211'
        option hwmode '11g'
        option path 'platform/10180000.wmac'
        option country 'PL'
        option disabled '0'
        option htmode 'HT40'
        option distance '3'
        option txpower '20'
        option channel '6'

config wifi-iface
        option device 'radio0'
        option mode 'ap'
        option ssid 'xxx'
        option network 'lan'
        option encryption 'psk2+ccmp'
        option key 'xxx'

Also it's connected with the issue of android devices loosing connectivity/dropping wifi even 1 meter next to router:
Fri Jul  7 00:32:11 2017 daemon.info hostapd: wlan0: STA xx:xx:xx:xx:xx:xx IEEE 802.11: authenticated
Fri Jul  7 00:32:11 2017 daemon.info hostapd: wlan0: STA xx:xx:xx:xx:xx:xx IEEE 802.11: associated (aid 2)
Fri Jul  7 00:32:11 2017 daemon.notice hostapd: wlan0: AP-STA-CONNECTED xx:xx:xx:xx:xx:xx
Fri Jul  7 00:32:11 2017 daemon.info hostapd: wlan0: STA xx:xx:xx:xx:xx:xx WPA: pairwise key handshake completed (RSN)
Fri Jul  7 00:32:51 2017 daemon.info hostapd: wlan0: STA xx:xx:xx:xx:xx:xx IEEE 802.11: disconnected due to excessive missing ACKs
Fri Jul  7 00:32:51 2017 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED xx:xx:xx:xx:xx:xx
Fri Jul  7 00:32:55 2017 daemon.info hostapd: wlan0: STA xx:xx:xx:xx:xx:xx IEEE 802.11: authenticated
Fri Jul  7 00:32:55 2017 daemon.info hostapd: wlan0: STA xx:xx:xx:xx:xx:xx IEEE 802.11: associated (aid 2)
Fri Jul  7 00:32:55 2017 daemon.notice hostapd: wlan0: AP-STA-CONNECTED xx:xx:xx:xx:xx:xx
Fri Jul  7 00:32:55 2017 daemon.info hostapd: wlan0: STA xx:xx:xx:xx:xx:xx WPA: pairwise key handshake completed (RSN)

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=896