[FS#176] Disapearing radios for ath9k introduced between August 31 and September 4th

[LEDE Bugs]

The following task has a new comment added:

FS#176 - Disapearing radios for ath9k introduced between August 31 and September 4th
User who did this - moeller0 (moeller0)

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Update for BSID loss on netgear wndr3700v2 with Atheros AR9280 Rev:2 radios. (the changes are also included as updates to comment #1, but to re-trigger the email function here is a new comment)

Definitions:
working: the radios stay visible and useable for at least around 24 hours
affected: the radios disappear and do not re-appear until the wifi command is issued at the router's CLI.

Testing: 
Move nexus5X into area of relative bad reception, disable mobile data and run netalyzr and wifi analyzer apps to generate siome traffic and see the BSIDs go away. Affected build will loose the radio in typically less than 5 minutes with this test. After issueing wifi the test is repeated. If the test does not make the radios go away the build is further tested with normal usage (which in affected build will also make the radios disappear in a few minutes to a few hours).

Tested versions (I will try to update this list):

**Working: radios stay enabled and useable:**

lede-r1212-20160801
lede-r1297-20160812
lede-r1398-20160822
lede-r1442-20160825-8859102
lede-r1462-20160829
lede-r1476-20160831
lede-r1481-20160902-1e72d1b-mac80211_add_a_powersave_handling_fix (no failure in 24h)



**Currently testing:**


lede-r1481-20160902-1e72d1b-mac80211_add_a_powersave_handling_fix (long term test)




**"Affected": radios disappear (seemingly partially triggered by moving into an area with bad reception)**

lede-r1482-20160902-372d0fe-ath9k_add_a_bunch_of_powersave_handling (no failures for 12 hours, 4 failures in 7 hours)
lede-r1483-20160902-a894a53-mac80211_add_fixes_for_dealing_with_unex (failures in 5 minutes)
lede-r1491-20160902-dbc9ee5-ath9k_fix_regression_in_tx_queueing_patc
lede-r1497-20160904
lede-r1512-20160905
lede-r1535-20160908
lede-r1600-20160915


Hypothesis:
r1482 somehow introduced a new or exposed an old and hidden bug for the wndr3700v2' radios, r1483 might either have introduced an easier way to trigger the offensive conditions, but that is conjecture...

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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=176#comment446