network.service: Add default route

Add the setting of the default route into this service. This is supposed
to replace gateway.service which should be removed, if this is merged.

The problem with two different services is, that the system looses the
route when network.service is stopped. Currently, gateway.service is
also stopped, because of a Requires= dependency, but not restarted, when
network.service is restarted. Downgrading the dependency to Wants=
wouldn't resolve the problem, because the system looses the route anyway
when the ip address is removed.

If we make sure, that we add the route every time we set the ip
address, we can restart network.service without loosing the default
route. The services are not independent anyway, because the gateway ip
address must be on a local network and thus match the ip address used by
this unit.

misc_systemd_units/network.service

@@ -9,6 +9,7 @@ RemainAfterExit=yes
 ExecStart=/usr/sbin/mxnetctl start
 ExecStart=/sbin/ip addr add ${MX_IPADDR}/20 broadcast 141.14.31.255 dev ${MX_NETDEV}
 ExecStart=/sbin/ip link set up dev ${MX_NETDEV}
+ExecStart=/sbin/ip route add default via 141.14.16.128
 ExecStop=/sbin/ip addr del ${MX_IPADDR}/20 dev ${MX_NETDEV}
 StandardOutput=syslog