add more radvd config

[rubo77]

this is our current config on vpn6.ffnord.net:

cat /etc/radvd.conf.d/interface-br-ffki.conf 
# managed for interface br-ffki
interface br-ffki
{
 AdvSendAdvert on;
 IgnoreIfMissing on;
 AdvDefaultLifetime 0;
 MaxRtrAdvInterval 200;

# prefix 2a03:2267:4e70::/64
# {
#   AdvPreferredLifetime 14400; # Here
#   AdvValidLifetime 86400; # Here
# };

 prefix fda1:384a:74de:4242:0000:0000:0000:0000/64
 {
   AdvPreferredLifetime 14400; # Here
   AdvValidLifetime 86400; # Here
 };

 RDNSS fda1:384a:74de:4242::ff06
 {
 };
};

[rubo77]

related #160