Previously with configuration WantedBy=network.target it could happen
that after enabling let's say zebra and bgpd and restarting the server
services won't be started. In case when no service pulls in
network.target quagga daemons won't start, because they are enabled
under network.target. This might be the case when only zebra is used
for configuring interfaces and other services like NM and initscripts
are disabled.
This commit also removes ordering dependency on syslog.target, since
this is redundant these days, because systemd-journald is early boot
service.
