join nameserver list with comma characters

templates/kea-dhcp4.conf.j2

@@ -61,7 +61,7 @@
                                                  "code": 6, 
                                                "space": "dhcp4", 
                                                "csv-format": true, 
-                                               "data": netclass.dns.nameservers.ipv4 }) -%}
+                                               "data": netclass.dns.nameservers.ipv4 | join(',') }) -%}
 {%-           endif -%}
 {%-         endif -%}
 {%-         if netclass.dns.domain is defined -%}

templates/kea-dhcp6.conf.j2

@@ -50,7 +50,7 @@
                                                "code": 23, 
                                                "space": "dhcp6", 
                                                "csv-format": true, 
-                                               "data": netclass.dns.nameservers.ipv6 }) -%}
+                                               "data": netclass.dns.nameservers.ipv6 | join(',') }) -%}
 {%-           endif -%}
 {%-         endif -%}
 {%-         if netclass.dns.domain is defined -%}