utils: tal_hexstr() helper.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

utils.c

@@ -0,0 +1,9 @@
+#include "utils.h"
+#include <ccan/str/hex/hex.h>
+
+char *tal_hexstr(const tal_t *ctx, const void *data, size_t len)
+{
+	char *str = tal_arr(ctx, char, hex_str_size(len));
+	hex_encode(data, len, str, hex_str_size(len));
+	return str;
+}