Install systemd services with autotools

Change-Id: I103bf3468d53578045593eac31b61f7e0248495e
diff --git a/debian/osmo-gbproxy.install b/debian/osmo-gbproxy.install
index 8272551..9c7fb77 100644
--- a/debian/osmo-gbproxy.install
+++ b/debian/osmo-gbproxy.install
@@ -1,3 +1,4 @@
+lib/systemd/system/osmo-gbproxy.service
 usr/bin/osmo-gbproxy
 usr/share/doc/osmo-sgsn/examples/osmo-gbproxy/osmo-gbproxy-legacy.cfg usr/share/doc/osmo-gbproxy/examples
 usr/share/doc/osmo-sgsn/examples/osmo-gbproxy/osmo-gbproxy.cfg usr/share/doc/osmo-gbproxy/examples