DDNS-scripts regression in 21.02.0 RC1 and RC2 and proposed fix/reversion

My router was successfully using the DDNS script for DuckDNS in 19.07, but after updating to 21.02.0 RC1 it stopped working. Tracing the issue showed that this commit broke it: https://github.com/openwrt/packages/commit/5b362932a7df5ce44ca3a8f4cf1d2b225ca8d5ae
which is discussed here https://github.com/openwrt/packages/pull/13183

I attempted to contact the person who created the pull request (@mrjoel) to ask him to try a different fix for the issue he experienced, but he has not responded. This issue was also discussed here: DDNS not working with PPPoE interface - #3 by Hikari but I didn't get a response to my request to revert there, so am trying again in this new thread.

Please consider this a request to revert the commit linked above for the next release.