jsonrpc: Add `msatoshi` argument to `sendonion` to annotate

While not directly necessary, it still feeds the `listpays` result, and so we
should pass it along if we can, so we don't have to rely solely on the
`amount_sent` field, which includes the fees.

Reported-by: Rusty Russell <@rustyrussell>

lightningd/pay.c

@@ -1179,6 +1179,7 @@ static struct command_result *json_sendonion(struct command *cmd,
 	struct lightningd *ld = cmd->ld;
 	const char *label, *b11str;
 	struct secret *path_secrets;
+	struct amount_msat *msat;
 	u64 *partid;
 
 	if (!param(cmd, buffer, params,
@@ -1189,6 +1190,7 @@ static struct command_result *json_sendonion(struct command *cmd,
 		   p_opt("shared_secrets", param_secrets_array, &path_secrets),
 		   p_opt_def("partid", param_u64, &partid, 0),
 		   p_opt("bolt11", param_string, &b11str),
+		   p_opt_def("msatoshi", param_msat, &msat, AMOUNT_MSAT(0)),
 		   NULL))
 		return command_param_failed();
 
@@ -1201,7 +1203,7 @@ static struct command_result *json_sendonion(struct command *cmd,
 				    failcode);
 
 	return send_payment_core(ld, cmd, payment_hash, *partid,
-				 first_hop, AMOUNT_MSAT(0), AMOUNT_MSAT(0),
+				 first_hop, *msat, AMOUNT_MSAT(0),
 				 label, b11str, &packet, NULL, NULL, NULL,
 				 path_secrets);
 }

plugins/libplugin-pay.c

@@ -1029,6 +1029,7 @@ static struct command_result *payment_createonion_success(struct command *cmd,
 	json_object_end(req->js);
 
 	json_add_sha256(req->js, "payment_hash", p->payment_hash);
+	json_add_amount_msat_only(req->js, "msatoshi", p->amount);
 
 	json_array_start(req->js, "shared_secrets");
 	secrets = p->createonion_response->shared_secrets;