adjust channel list to avoid use of SRD channels

SRD channels are only 25 mW and hence have short range, this is rarely
what users want.

site.conf

@@ -39,7 +39,7 @@
 
     wifi5 = {
         channel = 44,
-        outdoor_chanlist = "100-140",
+        outdoor_chanlist = "100-138",
         ap = {
             ssid = 'Freifunk',
             owe_ssid = 'owe.freifunk-stuttgart.de',