radvd on ppoe interface problem

[Droppie391]

Situation:
2 OPNsense firewall in Master-Slave configuration

wan interface PPPoE to ISP Titan Networks Germany
IPv4 and IPv6 configured and running
IPv6 settings:
- DHCPv6
- Request Prefix only (no static IPv6 address)
- Prefix-Length = 48

The wan link will come up with local-link addresses

lan interface set up with static address and a 64 Prefix-Length

Routing advertizements on the wan link cannot be configured as it has no static address
Routing advertizements on the lan link are turned to unmanaged so attached workstations will use SLAAC to get their IPv6 configuration ( ip address, prefix length, dns server etc)

due to a bug in the services.inc file, route advertizements are turned ON in radvd.conf for the wan interface. This causes radvd to crash (no prefix address nor netmask is returned)

work around: add an additional section to cancel the wan configuration in services.inc as follows (last elseif):

    /* handle manually configured DHCP6 server settings first */
    foreach ($config['dhcpdv6'] as $dhcpv6if => $dhcpv6ifconf) {
        if (!isset($config['interfaces'][$dhcpv6if]['enable'])) {
            continue;
        } elseif (isset($blacklist[$dhcpv6if])) {
            /* Do not put in the config an interface which is down */
            continue;
        } elseif (!isset($dhcpv6ifconf['ramode']) || $dhcpv6ifconf['ramode'] == 'disabled') {
            continue;
        } elseif (get_real_interface($dhcpv6if, "inet6") == 'igb0') {
         continue;
        }

please advise how to replace the last check to directly check up on the ppoe interface as igb0 is obviously hardware dependent.