network.service: Use environment file

All systems now have a file /etc/local/mxhost.conf with the host
specific IP address and network interface. Use that data in the unit
file.

Note, that this is not shell syntax. The difference between $VAR and
${VAR} is how the whitespaces inside VAR are handled. ${VAR} would be
"$VAR" in shell syntax.

We don't need the brackets, because the values are single words only.

However, unlike the shell, systemd would parse $MX_IPADDR/20 as an
environment variable named "MX_IPADDR/20". So we need the curlies at
that point to terminate the variable name. Use it everywhere for
readability and to avoid future errors.

misc_systemd_units/network.service

@@ -3,12 +3,13 @@ Description=Network Connectivity
 DefaultDependencies=no
 
 [Service]
+EnvironmentFile=/etc/local/mxhost.conf
 Type=oneshot
 RemainAfterExit=yes
 ExecStart=/usr/sbin/mxnetctl start
-ExecStart=/sbin/ip addr add 141.14.31.7/20 broadcast 141.14.31.255 dev net00
-ExecStart=/sbin/ip link set up dev net00
-ExecStop=/sbin/ip addr del 141.14.31.7/20 dev net00
+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}
+ExecStop=/sbin/ip addr del ${MX_IPADDR}/20 dev ${MX_NETDEV}
 StandardOutput=syslog
 
 [Install]