Revert "ifup@.service: Drop Before=network.target ordering"

Revert "ifup@.service: Drop Before=network.target ordering"

This reverts commit 27bb5c3851418590fe43179eb05ba511b42876d4.

For now we want this for shutdown order, to bring down ifup@.service after
network.target. Until we properly integrate ifupdown into
network-online.target, network-online.target and network.target are effectively
the same (on ifupdown only systems), so let's ignore the unnecessary boot
dependencies for now.