elementsd: disable dual-funding test; don't add non-witness utxo

Elementsd needs to be updated to v0.20.0 in order for this to work as
expected

tests/test_connection.py

@@ -819,6 +819,7 @@ def test_funding_toolarge(node_factory, bitcoind):
     l1.rpc.fundchannel(l2.info['id'], amount)
 
 
+@unittest.skipIf(TEST_NETWORK != 'regtest', 'elementsd doesnt yet support PSBT features we need')
 @unittest.skipIf(not EXPERIMENTAL_FEATURES, "dual-funding is experimental only")
 @unittest.skipIf(True, "df_opener.py requires wallycore")
 def test_v2_open(node_factory, bitcoind, chainparams):

wallet/reservation.c

@@ -295,6 +295,11 @@ static struct wally_psbt *psbt_using_utxos(const tal_t *ctx,
 						      &asset);
 		}
 
+		/* FIXME: as of 17 sept 2020, elementsd is *at most* at par
+		 * with v0.18.0 of bitcoind, which doesn't support setting
+		 * non-witness and witness utxo data for an input; remove this
+		 * check once elementsd can be updated */
+		if (!is_elements(chainparams)) {
 			/* If we have the transaction for this utxo,
 			 * add it to the PSBT as the non-witness-utxo field.
 			 * Dual-funded channels and some hardware wallets
@@ -303,6 +308,7 @@ static struct wally_psbt *psbt_using_utxos(const tal_t *ctx,
 			if (tx)
 				psbt_input_set_utxo(psbt, i, tx->wtx);
 		}
+	}
 
 	return psbt;
 }