lnwallet/btcwallet: Use signDesc.HashType when signing

Tis commit makes the btcwallet signer implementation use
signDesc.HashType instead of SigHashAll when signing
transactions. This will allow the creator of the transaction
to specify the sighash policy when creating the accompanying
sign descriptior.

lnwallet/btcwallet/signer.go

@@ -141,7 +141,7 @@ func (b *BtcWallet) SignOutputRaw(tx *wire.MsgTx,
 
 	amt := signDesc.Output.Value
 	sig, err := txscript.RawTxInWitnessSignature(tx, signDesc.SigHashes,
-		signDesc.InputIndex, amt, witnessScript, txscript.SigHashAll,
+		signDesc.InputIndex, amt, witnessScript, signDesc.HashType,
 		privKey)
 	if err != nil {
 		return nil, err
@@ -227,7 +227,7 @@ func (b *BtcWallet) ComputeInputScript(tx *wire.MsgTx,
 	// TODO(roasbeef): adhere to passed HashType
 	witnessScript, err := txscript.WitnessSignature(tx, signDesc.SigHashes,
 		signDesc.InputIndex, signDesc.Output.Value, witnessProgram,
-		txscript.SigHashAll, privKey, true)
+		signDesc.HashType, privKey, true)
 	if err != nil {
 		return nil, err
 	}