sms: Introduce a SMS queue that will be responsible for delivery

The SMSqueue will be responsible of sending to the user. It will
do so in a loop and will also try not to overload the BTS. This
means the throughput of SMS will be limited.
diff --git a/openbsc/src/bsc_hack.c b/openbsc/src/bsc_hack.c
index 4efc782..2b0af2e 100644
--- a/openbsc/src/bsc_hack.c
+++ b/openbsc/src/bsc_hack.c
@@ -274,6 +274,10 @@
 	signal(SIGUSR2, &signal_handler);
 	signal(SIGPIPE, SIG_IGN);
 
+	/* start the SMS queue */
+	if (sms_queue_start(bsc_gsmnet, 5) != 0)
+		return -1;
+
 	if (daemonize) {
 		rc = osmo_daemonize();
 		if (rc < 0) {