[FS#863] ath9k failure with AP+11s VIFs ("unsupported hw bitrate detected")

[LEDE Bugs]

The following task has a new comment added:

FS#863 - ath9k failure with AP+11s VIFs ("unsupported hw bitrate detected")
User who did this - FreifunkUFO (FreifunkUFO)

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here some freifunk people with 11s and same problem:
https://github.com/freifunk-gluon/gluon/issues/1148
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=863#comment3617