cfg80211: Add API to allow querying regdb for wmm_rule

In general regulatory self managed devices maintain their own
regulatory profiles thus it doesn't have to query the regulatory database
on country change.

ETSI has recently introduced a new channel access mechanism for 5GHz
that all wlan devices need to comply with.
These values are stored in the regulatory database.
There are self managed devices which can't maintain these
values on their own. Add API to allow self managed regulatory devices
to query the regulatory database for high band wmm rule.

Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
[johannes: fix documentation]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>