cfg80211: leave invalid channels on regdomain change

When the regulatory settings change, some channels might become invalid.
Disconnect interfaces acting on these channels, after giving userspace
code a grace period to leave them.

This mode is currently opt-in, and not all interface operating modes are
supported for regulatory-enforcement checks. A wiphy that wishes to use
the new enforcement code must specify an appropriate regulatory flag,
and all its supported interface modes must be supported by the checking
code.

Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Reviewed-by: Luis R. Rodriguez <mcgrof@suse.com>
[fix some indentation, typos]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>