gsm0408_test: initialize msgb talloc ctx

Change-Id: Ib26214add1932e93651c248cc09fbc68339b4dce
diff --git a/tests/gsm0408/gsm0408_test.c b/tests/gsm0408/gsm0408_test.c
index b469b30..f922a4f 100644
--- a/tests/gsm0408/gsm0408_test.c
+++ b/tests/gsm0408/gsm0408_test.c
@@ -149,6 +149,7 @@
 
 int main(int argc, char **argv)
 {
+	msgb_talloc_ctx_init(NULL, 0);
 	test_bearer_cap();
 	test_mid_from_tmsi();