fixup! gre/tun: init ip6gre

gre/files/tun.j2

 {%- for name, interface in pillar.ifaces.items() if 'mode' in interface -%}
-{%- if interface.mode == 'gretun' or interface.mode == 'gretun6' -%}
+{%- if interface.mode == 'gretun' or interface.mode == 'gretun6' %}
 auto {{ name }}
 iface {{ name }} inet tunnel
 {% if interface.mode == 'gretun' %}