contrib: Add systemd service file for osmo-hnbgw

Change-Id: I650bb5650b6d4f474e2040b57e6f78ee9d013825
diff --git a/contrib/systemd/osmo-hnbgw.service b/contrib/systemd/osmo-hnbgw.service
new file mode 100644
index 0000000..7aca29f
--- /dev/null
+++ b/contrib/systemd/osmo-hnbgw.service
@@ -0,0 +1,11 @@
+[Unit]
+Description=Osmocom Home Nodeb Gateway (OsmoHNBGW)
+
+[Service]
+Type=simple
+Restart=always
+ExecStart=/usr/bin/osmo-hnbgw -c /etc/osmocom/osmo-hnbgw.cfg
+RestartSec=2
+
+[Install]
+WantedBy=multi-user.target