transform backend template to macro

templates/kea-dhcp-backends.j2

-{% if dhcp_backend == "memfile" %}
+{% macro backends(ipversion="ipv4") %}
+{%   if dhcp_backend == "memfile" %}
     "lease-database": {
         "type": "memfile",
+{%     if ipversion == "ipv4" %}
         "name": "/var/db/kea/kea-leases4"
+{%     else %}
+        "name": "/var/db/kea/kea-leases6"
+{%     endif %}
     },
-{% elif dhcp_backend == "cassandra" %}
+{%   elif dhcp_backend == "cassandra" %}
     "lease-database": {
         "type": "cql",
         "keyspace": "{{ dhcp_db_dbname }}"
         "contact-points": "{{ dhcp_db_host }}"
-{%   if dhcp_db_port is defined %}
+{%     if dhcp_db_port is defined %}
         "port": "{{ dhcp_db_port }}"
-{%   endif %}
+{%     endif %}
     },
-{% else %}
+{%   else %}
     "lease-database": {
         "type": "{{ dhcp_backend }}",
         "name": "{{ dhcp_db_dbname }}",
         "host": "{{ dhcp_db_host }}",
-{%   if dhcp_db_port is defined %}
+{%     if dhcp_db_port is defined %}
         "port": "{{ dhcp_db_port }}"
-{%   endif %}
+{%     endif %}
         "user": "{{ dhcp_db_user }}"
         "password": "{{ dhcp_db_password | default("") }}"
     },
@@ -28,10 +33,11 @@
         "type": "{{ dhcp_backend }}",
         "name": "{{ dhcp_db_dbname }}",
         "host": "{{ dhcp_db_host }}",
-{%   if dhcp_db_port is defined %}
+{%     if dhcp_db_port is defined %}
         "port": "{{ dhcp_db_port }}"
-{%   endif %}
+{%     endif %}
         "user": "{{ dhcp_db_user }}"
         "password": "{{ dhcp_db_password | default("") }}"
     },
-{% endif %}
+{%   endif %}
+{% endmacro %}