add fixes to knot-dns

knot-dns/files/nextnode.conf.j2

 # upstream docu: https://www.knot-dns.cz/docs/latest/html/modules.html?highlight=subnet#using-subnets
 
-{{ salt['nextnode.knot_yaml']() }}
+{% for line in salt['nextnode.knot_yaml']() %}
+{{ line }}
+{%- endfor %}