When a link doesn't have VHT capability, before the rework
we'd have set IEEE80211_CONN_DISABLE_VHT, but now with the
linear progression of 'mode', we no longer have that. Add
an explicit check for VHT being supported, so we don't add
a zeroed VHT capabilities element where it shouldn't be.

Fixes: 310c8387 ("wifi: mac80211: clean up connection process")
Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240228094207.bfe4283bcde7.Ib70a558bc6bdbcec3d9e663079229dfcc2493682@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>