fff: advertise fdff:0::/64 to access web interface

This patch adds a prefix advertisment for each node. Every node get also
the IPs
* $prefix::MAC
* $prefix::link-local
* $prefix::1

::1 is duplicated so we need filtering to not forward data into the
network for ::1.

Signed-off-by: Tim Niemeyer <tim.niemeyer@mastersword.de>
Reviewed-by: Jan Kraus <mayosemmel@gmail.com>
Reviewed-by: Tobias Klaus <tk+ff@meskal.net>