Really ripngd should either leave groups on down interfaces, or keep

Really ripngd should either leave groups on down interfaces, or keep
track of on which interfaces joins have occurred.  This is complicated
by the possible lack of a clear behavior spec on whether interfaces
keep their joined group lists across a down/up/down transition.  (On
NetBSD, they do.)

2004-01-03  Greg Troxel  <gdt@ahi.ir.bbn.com>

        * ripng_interface.c (ripng_multicast_join): If IPV6_JOIN_GROUP
        returns EADDRINUSE, consider the join successful.  This happens
        when an interface goes down and comes back because
        ripng_multicast_leave does not invoke the LEAVE_GROUP operation if
        the interface is down.  Solves problem of ripng stopping working
        on an interface which goes down and then comes back up (on NetBSD).