Apparently RHEL-8 enables dhcp on all interfaces by default, so in theory we could stop using the dhcp-all-interfaces element in overcloud-full image builds and still get the desired behavior for first boot. RHEL-7 and earlier would only do dhcp on the first interface, which is why this element was required. Since this is no longer the case we should go ahead and remove this element.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (Red Hat OpenStack Platform 16.1.7 (Train) bug fix and enhancement advisory), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2021:3762