This value will be included in all IPv6 router advertisements sent
out this interface. Very short intervals are not recommended in
normal IPv6 operation. When a nondefault value is configured, the
configured time is both advertised and used by the router itself.
When value 0 is configured, 0 seconds (unspecified) advertised in
router advertisements and the value 1000 milliseconds is used for
the neighbor discovery activity of the router itself.