followup: restore service ordering state as previous

followup: restore service ordering state as previous

commit 214bc505acdeaa33c9b9b14b75e16f292f8d95f3 removed this by
mistake. While I fix it before detecting that (thank Wolfgang!) lets
restore it more like the state it was.

Add missing ordering:
  After=network-pre.target
    See systemd.special(7)'s description of this target
  After=systemd-sysctl.service
    ifupdown does the same - we want net.*.conf.default.*
    sysctl keys to apply to newly created interfaces
  After=systemd-modules-load.service
    ifupdown does the same, though this should be mostly
    optional as modules should be autoloaded anyway
  Before=network.target
    This is required to prevent services which require
    network to be started too early and listen on wrong
    addresses (iow. only on loopback or ipv4-only).
  Before=network-online.target
    See systemd.special(7)'s description. We are the
    provider of this target.
  Before=shutdown.target
    ifupdown does it this way, it also makes more sense
    given the Conflict entry, compared to the previous
    WantedBy entry in [Install]

Changed install section:
  WantedBy=multi-user.target
    I wasn't sure about this. ifupdown does this.
    basic.target didn't seem useful since we actually want:
  WantedBy=network-online.target
    We provide this, so we should be installed into it.
  removed WantedBy=network.target
    We strictly want to be ordered before this and instead
    are required by multi-user.target already.
  removed WantedBy=shutdown.target
    I didn't see the point.

Originally-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>