[FS#13] Ath9k AP stays up for connected clients but doesn't show in scan on new ones

[LEDE Bugs]

The following task has a new comment added:

FS#13 - Ath9k AP stays up for connected clients but doesn't show in scan on new ones
User who did this - Felix Fietkau (nbd)

----------
I pushed another fix you can test to my staging tree. It fixes some issues with calibration (which might play a role in these hangs).
----------

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=13#comment1113