[FS#171] Broken Wifi on (at least) ZBT WG2626 with latest LEDE

[LEDE Bugs]

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

User who did this - Kristian Evensen (kristrev) 

Attached to Project - LEDE Project
Summary - Broken Wifi on (at least) ZBT WG2626 with latest LEDE
Task Type - Bug Report
Category - Kernel
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - High
Priority - Very Low
Reported Version - All
Due in Version - Undecided
Due Date - Undecided
Details - Wifi on (at least) the ZBT WG2626 is broken with the latest LEDE built from source (both the 5 and 2.4GHz interface). I can configure the APs, the APs come up and are visible from the devices and I can authenticate with the APs. However, routing traffic seems to be broken. When capturing traffic I see the DHCP request and reply, but not reply is not received by any device. git bisect points to this commit as being the culprit: mac80211: fix packet loss on fq reordering (a194ffd4a89588bc75aeb9a27f59c36afd3d24bd). After reverting this commit (and c4bfb119d85bcd5faf569f9cc83628ba19f58a1f), wifi works as expected.

I tested my image on a couple of different 2626-devices I have to rule out hardware issues. I also made two different images, one with the latest mt76 in LEDE and one with the latest mt76 from the git repo. There was no difference in behavior. In addition, I also built an image for the Archer C7. It did not display any issues and worked as intended, so I guess the cause is in the interaction between the feature introduced in this commit and the mt76 driver.

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=171