Don't set another lighthouse hosts on lighthouse

ansible/project/roles/nebula/templates/config.yaml.j2

@@ -35,11 +35,12 @@ static_host_map:
 lighthouse:
   am_lighthouse: {{ addr_host.nebula_am_lighthouse }}
   interval: 60
+{% if not addr_host.nebula_am_lighthouse %}
   hosts:
 {% for host in nebula.lighthouses %}
     - {{ host.private }}
 {% endfor %}
-
+{% endif %}
   local_allow_list:
     interfaces:
       "tun.*": false