psbt_channel_funder+tapchannel: add remote max HTLC

We want to be able to dictate how many HTLCs the remote side can add to
the channel we create. We'll do the same for the responder side with a
channel acceptor in one of the following commits.

psbt_channel_funder.go

@@ -110,6 +110,7 @@ func (l *LndPbstChannelFunder) OpenChannel(ctx context.Context,
 			},
 		}),
 		lndclient.WithRemoteReserve(CustomChannelRemoteReserve),
+		lndclient.WithRemoteMaxHtlc(req.RemoteMaxHtlc),
 	)
 	if err != nil {
 		return nil, fmt.Errorf("unable to open channel with "+

tapchannel/aux_funding_controller.go

@@ -94,6 +94,11 @@ type OpenChanReq struct {
 	// PushAmt is the amount of BTC to push to the remote peer.
 	PushAmt btcutil.Amount
 
+	// RemoteMaxHtlc is the maximum number of HTLCs we allow the remote to
+	// add to the channel. If this is zero, then the default value defined
+	// by lnd (and dependent on the channel capacity) will be used.
+	RemoteMaxHtlc uint32
+
 	// PeerPub is the identity public key of the remote peer we wish to
 	// open the channel with.
 	PeerPub btcec.PublicKey