osmo-msc: track the use of talloc NULL memory contexts

Tracking NULL memory contexts allows one to detect memory chunks,
allocated outside the application's root context, which in most
cases are results of some mistake.

In b874486e8e the repotring of
NULL-context state was introduced, but without asking talloc
to track the use of NULL memory contexts it doesn't make sense.

Change-Id: I4b5e3946ee21c7d0ed6c66b1059dbce5ad312f88

src/osmo-msc/msc_main.c

@@ -521,6 +521,9 @@ int main(int argc, char **argv)
 {
 	int rc;
 
+	/* Track the use of talloc NULL memory contexts */
+	talloc_enable_null_tracking();
+
 	msc_vty_info.copyright	= osmomsc_copyright;
 
 	tall_msc_ctx = talloc_named_const(NULL, 1, "osmo_msc");