[tests] Fix building... add another stub...

diff --git a/tests/gsm0408/gsm0408_test.c b/tests/gsm0408/gsm0408_test.c
index c2f3f3f..8b3a376 100644
--- a/tests/gsm0408/gsm0408_test.c
+++ b/tests/gsm0408/gsm0408_test.c
@@ -83,3 +83,4 @@
 void gsm0411_send_sms(void) {}
 void lchan_auto_release(void) {}
 void page_request_stop(void) {}
+void paging_request_stop(void) {}