psbt: only compare a subset of psbt input/output fields

At some point, it's ok to add more extra info to a psbt and still not
have that be counted as 'diff'd.

common/psbt_open.c

@@ -72,8 +72,15 @@ static const u8 *linearize_input(const tal_t *ctx,
 
 	/* Sort the inputs, so serializing them is ok */
 	wally_map_sort(&psbt->inputs[0].unknowns, 0);
-	wally_map_sort(&psbt->inputs[0].keypaths, 0);
-	wally_map_sort(&psbt->inputs[0].signatures, 0);
+
+	/* signatures, keypaths, etc - we dont care if they change */
+	psbt->inputs[0].final_witness = NULL;
+	psbt->inputs[0].final_scriptsig_len = 0;
+	psbt->inputs[0].witness_script_len = 0;
+	psbt->inputs[0].redeem_script_len = 0;
+	psbt->inputs[0].keypaths.num_items = 0;
+	psbt->inputs[0].signatures.num_items = 0;
+
 
 	const u8 *bytes = psbt_get_bytes(ctx, psbt, &byte_len);
 
@@ -102,7 +109,12 @@ static const u8 *linearize_output(const tal_t *ctx,
 	psbt->num_outputs++;
 	/* Sort the outputs, so serializing them is ok */
 	wally_map_sort(&psbt->outputs[0].unknowns, 0);
-	wally_map_sort(&psbt->outputs[0].keypaths, 0);
+
+	/* We don't care if the keypaths change */
+	psbt->outputs[0].keypaths.num_items = 0;
+	/* And you can add scripts, no problem */
+	psbt->outputs[0].witness_script_len = 0;
+	psbt->outputs[0].redeem_script_len = 0;
 
 	const u8 *bytes = psbt_get_bytes(ctx, psbt, &byte_len);
 

lightningd/dual_open_control.c

@@ -218,7 +218,7 @@ openchannel2_changed_hook_serialize(struct openchannel2_psbt_payload *payload,
 	json_add_psbt(stream, "psbt", payload->psbt);
 	json_add_string(stream, "channel_id",
 			type_to_string(tmpctx, struct channel_id,
-				       &payload->rcvd->channel->cid));
+				       &payload->rcvd->cid));
 	json_object_end(stream);
 }