Comment 7 for bug 1629972

> ifdown -a --exclude=lo

Indeed, nicely spotted! So this would make a difference on machines which still have "lo" in /etc/network/interfaces (which hasn't been necessary/recommended since 2014), but I figure we still have too many places (installer/cloud image builder etc.) which write that. So adding --exclude=lo is correct for sure (even it might not completely fix this bug).