hlr.c: properly terminate the process on SIGTERM

As per the systemd.kill manual, when a service is going to be
stopped by systemd, the process will first be terminated via
SIGTERM. If then, after a delay, processes still remain, the
the termination request is repeated with the SIGKILL.

It was observed that osmo-hlr immediately terminates on SIGTERM,
leaving the SQLite database open. As a result, several temporary
files (such as hlr.db-shm, hlr.db-wal) remain, allowing the
further recovery:

  DDB ERROR <0001> db.c:86 (283) recovered 10 frames from WAL file

Let's properly handle SIGTERM in the same way as we handle SIGINT.

Change-Id: I1a4a48b95bbaed74ff5a03fb5797a44bdb1fcd3a
diff --git a/src/hlr.c b/src/hlr.c
index f374ccc..422a56d 100644
--- a/src/hlr.c
+++ b/src/hlr.c
@@ -612,8 +612,9 @@
 static void signal_hdlr(int signal)
 {
 	switch (signal) {
+	case SIGTERM:
 	case SIGINT:
-		LOGP(DMAIN, LOGL_NOTICE, "Terminating due to SIGINT\n");
+		LOGP(DMAIN, LOGL_NOTICE, "Terminating due to signal=%d\n", signal);
 		quit++;
 		break;
 	case SIGUSR1:
@@ -709,6 +710,7 @@
 
 	osmo_init_ignore_signals();
 	signal(SIGINT, &signal_hdlr);
+	signal(SIGTERM, &signal_hdlr);
 	signal(SIGUSR1, &signal_hdlr);
 
 	if (cmdline_opts.daemonize) {