bsc: Use the right connection for outgoing packets

This is needed for simple UDT messages where we do not have
a SCCP connection.
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_msc.c b/openbsc/src/osmo-bsc/osmo_bsc_msc.c
index 1ed0199..b2962a9 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_msc.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_msc.c
@@ -414,7 +414,7 @@
 			return;
 		}
 
-		sccp_write(msg, &sccp_ssn_bssap, &sccp_ssn_bssap, 0, NULL);
+		sccp_write(msg, &sccp_ssn_bssap, &sccp_ssn_bssap, 0, conn);
 		msgb_free(msg);
 		conn->is_authenticated = 1;
 	}