knot-dns: turn on edns-client-subnet in server section to enable geoip

https://www.knot-dns.cz/docs/latest/html/reference.html#edns-client-subnet

knot-dns/files/knot.conf.j2

@@ -11,6 +11,8 @@ server:
     listen: ::@53
     # User for running the server.
     user: knot:knot
+    # https://www.knot-dns.cz/docs/latest/html/reference.html#edns-client-subnet
+    edns-client-subnet: on
 log:
     # Log info and more serious events to syslog.
   - target: syslog