lightningd: print out support for channel_types in --list-features.

It's not a separate option, but lnprototest needs it to know to expect
the tlvs.

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

lightningd/options.c

@@ -761,6 +761,9 @@ static char *list_features_and_exit(struct lightningd *ld)
 	const char **features = list_supported_features(tmpctx, ld->our_features);
 	for (size_t i = 0; i < tal_count(features); i++)
 		printf("%s\n", features[i]);
+#if EXPERIMENTAL_FEATURES
+	printf("supports_open_accept_channel_types\n");
+#endif
 	exit(0);
 }