nat: Print the unknown byte as a integer instead of charachter

The value might be a non printable one.
diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index 7effe48..81d4de9 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -107,7 +107,7 @@
 	data_length = TLVP_LEN(&tp, GSM0808_IE_CELL_IDENTIFIER_LIST);
 	data = TLVP_VAL(&tp, GSM0808_IE_CELL_IDENTIFIER_LIST);
 	if (data[0] !=  CELL_IDENT_LAC) {
-		LOGP(DNAT, LOGL_ERROR, "Unhandled cell ident discrminator: %c\n", data[0]);
+		LOGP(DNAT, LOGL_ERROR, "Unhandled cell ident discrminator: %d\n", data[0]);
 		return NULL;
 	}