Comment 9 for bug 1721223

Xnox pointed out that the above net.ipv4.conf.all.promote_secondaries=1 is actually a default of systemd (added in https://github.com/systemd/systemd/commit/ad8bc9ea508740074cead005aa3cfd1ba10a5dac). This looks like we will enable it for everybody via a systemd SRU.