systemd: Add service unit for eturnal.service

Taken [from upstream][1].

With `LogsDirectory=eturnal`, eturnal currently logs to
`/var/log/eturnal/eturnal.log`.

[1]: https://github.com/processone/eturnal/blob/master/config/eturnal.service

install.sh

@@ -161,6 +161,7 @@ install_data misc_systemd_units/named.service            "$DESTDIR$systemdunitdi
 install_data misc_systemd_units/tonerlow-cupsd.service   "$DESTDIR$systemdunitdir/tonerlow-cupsd.service"
 install_data misc_systemd_units/baucamhttpd.service      "$DESTDIR$systemdunitdir/baucamhttpd.service"
 install_data misc_systemd_units/getcams.service          "$DESTDIR$systemdunitdir/getcams.service"
+install_data misc_systemd_units/eturnal.service          "$DESTDIR$systemdunitdir/eturnal.service"
 install_exec blink/blinkd.py                             "$DESTDUR$udev_helperdir/blinkd.py"
 install_data blink/blinkd.service                        "$DESTDIR$systemdunitdir/blinkd.service"
 install_data blink/51-blink.rules                        "$DESTDIR$udev_rulesdir/51-blink.rules"

misc_systemd_units/eturnal.service

@@ -0,0 +1,26 @@
+[Unit]
+Description=eturnal STUN/TURN server
+Wants=epmd.service
+After=epmd.service network.target
+Documentation=https://eturnal.net/documentation/
+Documentation=https://github.com/processone/eturnal/blob/1.4.1/README.md
+Documentation=https://github.com/processone/eturnal/blob/1.4.1/CHANGELOG.md
+
+[Service]
+Type=notify
+User=eturnprj
+ExecStart=/project/eturnal/eturnal-current/bin/eturnalctl foreground
+ExecReload=/project/eturnal/eturnal-current/bin/eturnalctl reload
+ExecStop=/project/eturnal/eturnal-current/bin/eturnalctl stop
+Restart=on-failure
+RestartSec=3
+WatchdogSec=30
+LimitNOFILE=50000
+RuntimeDirectory=eturnal
+LogsDirectory=eturnal
+ProtectSystem=full
+NoNewPrivileges=true
+AmbientCapabilities=CAP_NET_BIND_SERVICE
+
+[Install]
+WantedBy=multi-user.target