VyOS DNS forwarding via dhcp bug

--- dns_forwarding.py.bak	2021-09-25 12:16:53.914360438 +1000
+++ dns_forwarding.py	2021-09-25 12:26:29.155436648 +1000
@@ -157,8 +157,8 @@
             hc.delete_name_server_tags_recursor(['system'])

         # add dhcp nameserver tags for configured interfaces
-        if 'system_name_server_dhcp' in dns:
-            for interface in dns['system_name_server_dhcp']:
+        if 'system_name_server' in dns:
+            for interface in dns['system_name_server']:
                 hc.add_name_server_tags_recursor(['dhcp-' + interface,
                                                   'dhcpv6-' + interface ])