sms: Begin sending SMS messages, handle failures

The sms queue will attempt to send one SMS per subscriber
to fill all the available slots. It will handle the case
where paging has not started, timed out or if there was
any kind of other failure. It is also retransmitting SMS
in case of failures.
diff --git a/openbsc/include/openbsc/sms_queue.h b/openbsc/include/openbsc/sms_queue.h
index d377aca..d048566 100644
--- a/openbsc/include/openbsc/sms_queue.h
+++ b/openbsc/include/openbsc/sms_queue.h
@@ -2,7 +2,9 @@
 #define SMS_QUEUE_H
 
 struct gsm_network;
+struct gsm_sms_queue;
 
 int sms_queue_start(struct gsm_network *, int in_flight);
+int sms_queue_trigger(struct gsm_sms_queue *);
 
 #endif