After reading that wifi channel 13 should now be working in the rpi3 I tried with the latest 4.4.11 kernel from arch, but no luck.
I then tried the latest raspbian which has a 4.4.9 kernel. There I can see that both channels 12 & 13 are working (using sudo iw list) and indeed I set that NetworkManager can see my access point.
Scanned some posts for info what might be missing and saw only that
sudo iw reg set GB
should work or alternatively I should configure country=GB in the wpa_supplicant.conf file
I tried both of these and neither seems to make any difference.
Does anybody know how to get the rpi3 to see channels 12 & 13?