lnwallet: make BlockChainIO.GetUTXO take cancel chan

Use quit channels as cancel chan for call to GetUTXO.

lnwallet/btcwallet/blockchain.go

@@ -38,7 +38,7 @@ func (b *BtcWallet) GetBestBlock() (*chainhash.Hash, int32, error) {
 //
 // This method is a part of the lnwallet.BlockChainIO interface.
 func (b *BtcWallet) GetUtxo(op *wire.OutPoint, pkScript []byte,
-	heightHint uint32) (*wire.TxOut, error) {
+	heightHint uint32, cancel <-chan struct{}) (*wire.TxOut, error) {
 
 	switch backend := b.chain.(type) {
 

lnwallet/interface.go

@@ -268,8 +268,10 @@ type BlockChainIO interface {
 	// script that the outpoint creates. In the case that the output is in
 	// the UTXO set, then the output corresponding to that output is
 	// returned.  Otherwise, a non-nil error will be returned.
-	GetUtxo(op *wire.OutPoint, pkScript []byte,
-		heightHint uint32) (*wire.TxOut, error)
+	// As for some backends this call can initiate a rescan, the passed
+	// cancel channel can be closed to abort the call.
+	GetUtxo(op *wire.OutPoint, pkScript []byte, heightHint uint32,
+		cancel <-chan struct{}) (*wire.TxOut, error)
 
 	// GetBlockHash returns the hash of the block in the best blockchain
 	// at the given height.

lnwallet/wallet.go

@@ -974,7 +974,7 @@ func (l *LightningWallet) handleFundingCounterPartySigs(msg *addCounterPartySigs
 			}
 			output, err := l.Cfg.ChainIO.GetUtxo(
 				&txin.PreviousOutPoint,
-				pkScript, 0,
+				pkScript, 0, l.quit,
 			)
 			if output == nil {
 				msg.err <- fmt.Errorf("input to funding tx "+