wifi: cfg80211: fix CQM for non-range use

My prior race fix here broke CQM when ranges aren't used, as
the reporting worker now requires the cqm_config to be set in
the wdev, but isn't set when there's no range configured.

Rather than continuing to special-case the range version, set
the cqm_config always and configure accordingly, also tracking
if range was used or not to be able to clear the configuration
appropriately with the same API, which was actually not right
if both were implemented by a driver for some reason, as is
the case with mac80211 (though there the implementations are
equivalent so it doesn't matter.)

Also, the original multiple-RSSI commit lost checking for the
callback, so might have potentially crashed if a driver had
neither implementation, and userspace tried to use it despite
not being advertised as supported.

Cc: stable@vger.kernel.org
Fixes: 4a4b8169 ("cfg80211: Accept multiple RSSI thresholds for CQM")
Fixes: 37c20b2e

 ("wifi: cfg80211: fix cqm_config access race")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>