ieee80211_vht_get_vhtflags() is checking the htinfo IE for the
20/40MHz flag as part of deciding valid channel widths.

However, in the hostapd path, the ASSOC_REQ/REASSOC_REQ path
will parse the IEs, do some HT/VHT setup, then call
ieee80211_ht_updatehtcap_final(). In a HT ASSOC/REASSOC request
there won't be a HTINFO IE, however ieee80211_vht_get_vhtflags()
still checks for it, leading to a panic.

Instead, treat it as if we don't yet know if it's HT40 or not.
I'm not sure if we should do that or have it just do
_RETURN_CHAN_BITS(0).