mac80211: minstrel_ht: do not always skip ht rates vht_only is true

When CONFIG_MAC80211_RC_MINSTREL_VHT is set, the module param
minstrel_vht_only tells minstrel_ht whether to allow the mix of ht rates
with vht rates.
ATM, minstrel_ht skips ht rates when minstrel_vht_only is true, but it does
that even if vht is not supported, which makes the sta rates fallback to
legacy as no ht rate gets enabled.

Fixes: 9208247d ("mac80211: minstrel_ht: add basic support for VHT rates <= 3SS@80MHz")
Signed-off-by: Karl Beldan <karl.beldan@rivierawaves.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>