msc_vlr_tests: better err logging for dtap msgs

Change-Id: I3edd90be40555dd648e9f16db5b6040665a19a95
diff --git a/tests/msc_vlr/msc_vlr_tests.c b/tests/msc_vlr/msc_vlr_tests.c
index de4913a..e00c337 100644
--- a/tests/msc_vlr/msc_vlr_tests.c
+++ b/tests/msc_vlr/msc_vlr_tests.c
@@ -254,8 +254,10 @@
 
 	/* Mask the sequence number out before comparing */
 	msg->data[1] &= 0x3f;
-	if (!msgb_eq_data_print(msg, dtap_tx_expected->data, dtap_tx_expected->len))
+	if (!msgb_eq_data_print(msg, dtap_tx_expected->data, dtap_tx_expected->len)) {
+		btw("Expected %s", osmo_hexdump(dtap_tx_expected->data, dtap_tx_expected->len));
 		abort();
+	}
 
 	btw("DTAP matches expected message");