sms: Add a way to always route SMS through SMPP systems

default-route would only be looked at after there has been
no subscriber in the local database. Depending on the setup
this is not what one wants. This has been discussed at the
OsmoDevCon and there have been hacks in some branches. Let's
introduce a VTY command to select if SMPP should be consulted
first and then fallback to the current behavior.
diff --git a/openbsc/src/libmsc/smpp_smsc.h b/openbsc/src/libmsc/smpp_smsc.h
index 8d31b2b..3dd6562 100644
--- a/openbsc/src/libmsc/smpp_smsc.h
+++ b/openbsc/src/libmsc/smpp_smsc.h
@@ -92,6 +92,7 @@
 	uint16_t listen_port;
 	char system_id[SMPP_SYS_ID_LEN+1];
 	int accept_all;
+	int smpp_first;
 	struct osmo_smpp_acl *def_route;
 	void *priv;
 };
@@ -137,6 +138,8 @@
 struct gsm_sms;
 struct gsm_subscriber_connection;
 
+int smpp_route_smpp_first(struct gsm_sms *sms,
+			    struct gsm_subscriber_connection *conn);
 int smpp_try_deliver(struct gsm_sms *sms,
 			    struct gsm_subscriber_connection *conn);
 #endif