I had a closer look at how and where ifupdown recipe is used, and from what I see it isn't:
every configuration is relying on busybox to provide the same utilities. That's why the failure is seen only in world builds :)
Should we drop the ifupdown recipe?
which includes ifupdown only if systemd is not in use.
However that packagegroup is not used in any images, and the only test for it is in lib/oeqa/selftest/cases/imagefeatures.py
which does enable systemd, so that doesn't pull in ifupdown either.
This means ifupdown isn't runtime-tested now, and probably hasn't been tested for a while.