lightningd: don't cap spendable_msat/receivable_msat for wumbo channels.

If we both support large channels, we can actually send giant HTLCs.

This, in turn, fixes pay (which relies on this field!).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: Plugins: `pay` now knows it can use locally-connected wumbo channels for large payments.
Fixes: ElementsProject#5250
Fixes: ElementsProject#5417

lightningd/peer_control.c

@@ -613,6 +613,7 @@ static void subtract_received_htlcs(const struct channel *channel,
 struct amount_msat channel_amount_spendable(const struct channel *channel)
 {
 	struct amount_msat spendable;
+	bool wumbo;
 
 	/* Compute how much we can send via this channel in one payment. */
 	if (!amount_msat_sub_sat(&spendable,
@@ -636,16 +637,23 @@ struct amount_msat channel_amount_spendable(const struct channel *channel)
 			     channel->channel_info.their_config.htlc_minimum))
 		return AMOUNT_MSAT(0);
 
+	wumbo = feature_negotiated(channel->peer->ld->our_features,
+				   channel->peer->their_features,
+				   OPT_LARGE_CHANNELS);
+
 	/* We can't offer an HTLC over the max payment threshold either. */
-	if (amount_msat_greater(spendable, chainparams->max_payment))
+	if (amount_msat_greater(spendable, chainparams->max_payment)
+	    && !wumbo) {
 		spendable = chainparams->max_payment;
+	}
 
 	return spendable;
 }
 
 struct amount_msat channel_amount_receivable(const struct channel *channel)
 {
 	struct amount_msat their_msat, receivable;
+	bool wumbo;
 
 	/* Compute how much we can receive via this channel in one payment */
 	if (!amount_sat_sub_msat(&their_msat,
@@ -672,9 +680,15 @@ struct amount_msat channel_amount_receivable(const struct channel *channel)
 	if (amount_msat_less(receivable, channel->our_config.htlc_minimum))
 		return AMOUNT_MSAT(0);
 
+	wumbo = feature_negotiated(channel->peer->ld->our_features,
+				   channel->peer->their_features,
+				   OPT_LARGE_CHANNELS);
+
 	/* They can't offer an HTLC over the max payment threshold either. */
-	if (amount_msat_greater(receivable, chainparams->max_payment))
+	if (amount_msat_greater(receivable, chainparams->max_payment)
+	    && !wumbo) {
 		receivable = chainparams->max_payment;
+	}
 
 	return receivable;
 }

tests/test_connection.py

@@ -3407,7 +3407,6 @@ def test_pay_disconnect_stress(node_factory, executor):
 
 @pytest.mark.openchannel('v1')
 @pytest.mark.openchannel('v2')
-@pytest.mark.xfail(strict=True)
 def test_wumbo_channels(node_factory, bitcoind):
     l1, l2, l3 = node_factory.get_nodes(3,
                                         opts=[{'large-channels': None},