mac80211: fill low rate even for HAS_RATE_CONTROL

If HW advertises it has rate control, we skip all of the
rate control assignments, but sometimes the data we have
here is useful, especially so that we don't have to do
the lookups again on which rates are configured and are
supported.

So do the low rate assignment anyway to help out drivers
that might need it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>