mac80211: disable VHT for TDLS

TDLS VHT support requires some more information elements during setup.
While these are not there, mask out the peer's VHT capabilities so that
VHT rates are not mistakenly used.

Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>