kea-dhcp6 does not log client classes

With configuration and traffic that are as similar as possible for v4 and v6, kea-dhcp4 logs two subsequent lines showing the assignment to KNOWN or UNKNOWN from the first pass of classification, and then the the assignment to the rest of the classes from the second pass of classification. kea-dhcp6 is missing the second log line.

DHCP4_CLASS_ASSIGNED [hwtype=1 08:00:27:b0:c5:02], cid=[11:08:00:27:b0:c5:02], tid=0x5097a7: client packet has been assigned to the following class(es): UNKNOWN DHCP4_CLASS_ASSIGNED [hwtype=1 08:00:27:b0:c5:02], cid=[11:08:00:27:b0:c5:02], tid=0x5097a7: client packet has been assigned to the following class(es): ALL, HA_server1, gold, UNKNOWN

DHCP6_CLASS_ASSIGNED duid=[00:03:00:01:08:00:27:b0:c5:02], tid=0xb90f3d: client packet has been assigned to the following class(es): UNKNOWN

dhcp4_srv.cc has the following code in Dhcpv4Exchange::Dhcpv4Exchange, while dhcp6_srv.cc does not have an equivalent in its Dhcpv6Srv::initContext counterpart.

    const ClientClasses& classes = query_->getClasses();
    if (!classes.empty()) {
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_ASSIGNED)
            .arg(query_->getLabel())
            .arg(classes.toText());
    }