Upstream tries to use only IPV6_PKTINFO to specify the outgoing interface index, but our kernel doesn't support this. This lead upstream to add a workaround for "bogus BSDs", namely set sin6_scope_id in dhclient mode. But dhcpd/dhcrelay are affected by the same problem, so always set sin6_scope_id. Issue reported & initial diff proposed by Marc Peters, maintainer timeout.