cfg80211: use wiphy DFS domain if it is self-managed

Currently during CAC start or other radar events, the DFS
domain is fetched from cfg based on global DFS domain,
even if the wiphy regdomain disagrees.

But this could be different in case of self managed wiphy's
in case the self managed driver updates its database or supports
regions which has DFS domain set to UNSET in cfg80211 local
regdomain.

So for explicitly self-managed wiphys, just use their DFS
domain.

Signed-off-by: Sriram R <srirrama@codeaurora.org>
Link: https://lore.kernel.org/r/1629934730-16388-1-git-send-email-srirrama@codeaurora.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>