SMPP: Implement transaction mode for SUBMIT-SM

WARNING: if the ESME disconnects, osmo_esme gets freed, and
sms->smpp.esme might point to invalid/unallocated memory!
diff --git a/openbsc/src/libmsc/smpp_smsc.h b/openbsc/src/libmsc/smpp_smsc.h
index 500fbc3..8cdd2e7 100644
--- a/openbsc/src/libmsc/smpp_smsc.h
+++ b/openbsc/src/libmsc/smpp_smsc.h
@@ -46,6 +46,9 @@
 
 int smpp_smsc_init(struct smsc *smsc, uint16_t port);
 
+int smpp_tx_submit_r(struct osmo_esme *esme, uint32_t sequence_nr,
+		     uint32_t command_status, char *msg_id);
+
 int handle_smpp_submit(struct osmo_esme *esme, struct submit_sm_t *submit,
 			struct submit_sm_resp_t *submit_r);