alpine: don’t disable IPv6 autoconf on loopback interface

Not sure if it makes a difference but let’s keep the generated config
minimal.

roles/alpine/templates/interfaces.j2

@@ -47,7 +47,7 @@ iface {{ iface.name }}
 {% endfor -%}
 
 {# disable SLAAC if we have a manually set IPv6 address #}
-{% if iface.ip_addresses | selectattr("family.value", "==", 6) %}
+{% if iface.ip_addresses | selectattr("family.value", "==", 6) and iface.name != "lo" %}
     pre-up echo 0 > /proc/sys/net/ipv6/conf/$IFACE/autoconf
 {% endif %}