libmsc/gsm_09_11.c: do not suppress rc of gsup_client_mux_tx()

Change-Id: Ide2440188fb6fe1c54681fef8ec4fed9e6da66e2
diff --git a/src/libmsc/gsm_09_11.c b/src/libmsc/gsm_09_11.c
index df0a9b4..79fcb5a 100644
--- a/src/libmsc/gsm_09_11.c
+++ b/src/libmsc/gsm_09_11.c
@@ -242,7 +242,7 @@
 	if (msg_type == GSM0480_MTYPE_REGISTER)
 		rate_ctr_inc(&net->msc_ctrs->ctr[MSC_CTR_NC_SS_MO_ESTABLISHED]);
 
-	return 0;
+	return rc;
 
 error:
 	/* Abort transaction on DTAP-interface */