mac80211: TDLS: always downgrade invalid chandefs

Even if the current chandef width is equal to the station's max-BW, it
doesn't mean it's a valid width for TDLS. Make sure to always check
regulatory constraints in these cases.

Fixes: 0fabfaaf ("mac80211: upgrade BW of TDLS peers when possible")
Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>