systemd service: add save_log_tail

Change-Id: I36d149d1dbfe30a4e51122e671ab801b6fd18c74
diff --git a/contrib/systemd/osmo-mgw.service b/contrib/systemd/osmo-mgw.service
index f75277e..65150c9 100644
--- a/contrib/systemd/osmo-mgw.service
+++ b/contrib/systemd/osmo-mgw.service
@@ -6,6 +6,7 @@
 Restart=always
 ExecStart=/usr/bin/osmo-mgw -s -c /etc/osmocom/osmo-mgw.cfg
 RestartSec=2
+ExecStopPost=/usr/local/bin/save_log_tail osmo-mgw
 
 [Install]
 WantedBy=multi-user.target