Treat SIGTERM just like SIGINT in our programs

When somebody kills the process, it's best to handle the signal
and to use the opportunity for some cleanup.  We always did this
in the NITB on SIGINT, but never on SIGTERM. Let's change it.

Change-Id: Iea6804325a6575ceab5edfd28dd20249462f143b
diff --git a/src/gprs/gb_proxy_main.c b/src/gprs/gb_proxy_main.c
index 69a93b6..caff27f 100644
--- a/src/gprs/gb_proxy_main.c
+++ b/src/gprs/gb_proxy_main.c
@@ -98,6 +98,7 @@
 
 	switch (signal) {
 	case SIGINT:
+	case SIGTERM:
 		osmo_signal_dispatch(SS_L_GLOBAL, S_L_GLOBAL_SHUTDOWN, NULL);
 		sleep(1);
 		exit(0);
@@ -232,6 +233,7 @@
 	msgb_talloc_ctx_init(tall_bsc_ctx, 0);
 
 	signal(SIGINT, &signal_handler);
+	signal(SIGTERM, &signal_handler);
 	signal(SIGABRT, &signal_handler);
 	signal(SIGUSR1, &signal_handler);
 	signal(SIGUSR2, &signal_handler);