contrib: Change systemd requirements so the services connect properly

Change-Id: Ib1b3c640ddd81927a60ee307c4b0cb90fd83eebe
diff --git a/contrib/systemd/osmo-sgsn.service b/contrib/systemd/osmo-sgsn.service
index 674d786..bf6a8e0 100644
--- a/contrib/systemd/osmo-sgsn.service
+++ b/contrib/systemd/osmo-sgsn.service
@@ -1,5 +1,8 @@
 [Unit]
 Description=OpenBSC SGSN
+Wants=osmo-hlr.service
+After=osmo-hlr.service
+After=osmo-hnbgw.service
 
 [Service]
 Type=simple