nat: Print the SCCP ref's as hex numbers

This allows to more easily compare the numbers with traces
seen in wireshark.
diff --git a/openbsc/src/nat/bsc_nat_vty.c b/openbsc/src/nat/bsc_nat_vty.c
index 2ec5e34..ad33fd6 100644
--- a/openbsc/src/nat/bsc_nat_vty.c
+++ b/openbsc/src/nat/bsc_nat_vty.c
@@ -75,7 +75,7 @@
 {
 	struct sccp_connections *con;
 	llist_for_each_entry(con, &_nat->sccp_connections, list_entry) {
-		vty_out(vty, "SCCP for BSC: %d BSC ref: %u Local ref: %u MSC/BSC mux: 0x%x/0x%x%s",
+		vty_out(vty, "SCCP for BSC: %d BSC ref: 0x%x Local ref: 0x%x MSC/BSC mux: 0x%x/0x%x%s",
 			con->bsc->lac,
 			sccp_src_ref_to_int(&con->real_ref),
 			sccp_src_ref_to_int(&con->patched_ref),