The RFE [0] implemented iPXE chainloading support for IPv4. In order to complete the work we also need to implement it for IPv6.

There are some differences in how OVN DHCP should behave for these two versions:

1) For IPv4, OVN DHCP will look for option 175. If set it will return "bootfile_name" if unset it will return "bootfile_name_alt" (see RFE [0] for more details)

2) For IPv6, instead of looking for option 175 OVN DHCP should look at the "user class" field from the DHCP request and see if it's set to "iPXE" [1][2].

[0] https://bugzilla.redhat.com/show_bug.cgi?id=1765506
[1] https://github.com/openstack/neutron/blob/a7010e9c4e844940ef33aae3309ca4e323bef78e/neutron/agent/linux/dhcp.py#L393-L394
[2] https://datatracker.ietf.org/doc/html/rfc3315#section-22.15