layer23: modem: Unregister registered callbacks upon app exit

It's just a good practice to delete all resources allocated during startup.
The main aim here is to keep resemblance to what the mobile app is doing,
so that they can slowly be merged and some functionalities from the mobile app can be
added to the modem app, like shutting down the MS without killing the process eventually.

Change-Id: I5a641fa3dadb6ea7346b25a20215896ab32eb805
---
M src/host/layer23/src/modem/app_modem.c
1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/src/host/layer23/src/modem/app_modem.c b/src/host/layer23/src/modem/app_modem.c
index 211621e..12ac4ae 100644
--- a/src/host/layer23/src/modem/app_modem.c
+++ b/src/host/layer23/src/modem/app_modem.c
@@ -114,8 +114,8 @@
 	memset(&app_data, 0x00, sizeof(app_data));
 }
 
-static int signal_cb(unsigned int subsys, unsigned int signal,
-		     void *handler_data, void *signal_data)
+static int global_signal_cb(unsigned int subsys, unsigned int signal,
+			    void *handler_data, void *signal_data)
 {
 	struct osmocom_ms *ms;
 
@@ -151,11 +151,19 @@
 	return 0;
 }
 
+/* global exit */
+static int _modem_exit(void)
+{
+	osmo_signal_unregister_handler(SS_GLOBAL, &global_signal_cb, NULL);
+	return 0;
+}
+
 int l23_app_init(void)
 {
 	int rc;
 
 	l23_app_start = _modem_start;
+	l23_app_exit = _modem_exit;
 
 	log_set_category_filter(osmo_stderr_target, DLGLOBAL, 1, LOGL_DEBUG);
 	log_set_category_filter(osmo_stderr_target, DLCSN1, 1, LOGL_DEBUG);
@@ -189,7 +197,7 @@
 		return rc;
 	}
 
-	osmo_signal_register_handler(SS_L1CTL, &signal_cb, NULL);
+	osmo_signal_register_handler(SS_L1CTL, &global_signal_cb, NULL);
 	lapdm_channel_set_l3(&app_data.ms->lapdm_channel, &modem_grr_rslms_cb, app_data.ms);
 	return 0;
 }

