[nat] Remove parameter that is never accessed directly

The msgb needs to be around when we access the parsed structure
but that needs to be guranteed by the caller handing out the parsed
structure.
diff --git a/openbsc/tests/bsc-nat/bsc_nat_test.c b/openbsc/tests/bsc-nat/bsc_nat_test.c
index adc8a19..ca9fbd4 100644
--- a/openbsc/tests/bsc-nat/bsc_nat_test.c
+++ b/openbsc/tests/bsc-nat/bsc_nat_test.c
@@ -294,7 +294,7 @@
 		fprintf(stderr, "Con should not exist %p\n", con_found);
 		abort();
 	}
-	rc = create_sccp_src_ref(con, msg, parsed);
+	rc = create_sccp_src_ref(con, parsed);
 	if (rc != 0) {
 		fprintf(stderr, "Failed to create a ref\n");
 		abort();