To quote someone here:
The link also includes a patch to change this functionality but it is for hostapd 0.7.3 and the version on the Bubba is 0.7.2. This patch may now be part of the official code, I don't know.Why I'm not able to force 40MHz operation in my apartment? OK, I can "hear" neighboring
APs through the concrete walls with low signal quality, so what? This is my apartment, not
neighbors. And even if we share walls or floor, I'm still want to use 40MHz like the
neighbor did.
So my request is, can we get this patch applied to a version of hostapd available on the Bubba? I might have a go at patching and building a version myself and will report back here if I do.