You are actually right. I did set it to "DE" with iw, but wpa_supplicant
had a setting country="de". I just fixed that and will soon see if the
problem disappears.
Still, the warning shouldn't look like a bad kernel bug, but rather an
advisory to the user to set something sane. What confuses me even more
is that this has been set to DE afterwards:
$ dmesg | grep cfg80211:\ Calling\ CRDA
cfg80211: Calling CRDA to update world regulatory domain
cfg80211: Calling CRDA for country: de
cfg80211: Calling CRDA for country: DE
cfg80211: Calling CRDA to update world regulatory domain
cfg80211: Calling CRDA for country: DE
cfg80211: Calling CRDA to update world regulatory domain
cfg80211: Calling CRDA for country: DE
cfg80211: Calling CRDA to update world regulatory domain
cfg80211: Calling CRDA for country: DE
cfg80211: Calling CRDA to update world regulatory domain
cfg80211: Calling CRDA for country: DE
cfg80211: Calling CRDA to update world regulatory domain
cfg80211: Calling CRDA for country: DE
The AP has been playing with the regdom as well, I lost track of what
has been set where in this mess.