peer: add channel close fee negotiation

This commit adds the fee negotiation procedure performed
on channel shutdown. The current algorithm picks an ideal
a fee based on the FeeEstimator and commit weigth, then
accepts the remote's fee if it is at most 50%-200% away
from the ideal. The fee negotiation procedure is similar
both as sender and receiver of the initial shutdown
message, and this commit also make both sides use the
same code path for handling these messages.

mock.go

@@ -0,0 +1,154 @@
+package main
+
+import (
+	"github.com/lightningnetwork/lnd/chainntnfs"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/roasbeef/btcd/btcec"
+	"github.com/roasbeef/btcd/chaincfg/chainhash"
+	"github.com/roasbeef/btcd/txscript"
+	"github.com/roasbeef/btcd/wire"
+	"github.com/roasbeef/btcutil"
+)
+
+type mockSigner struct {
+	key *btcec.PrivateKey
+}
+
+func (m *mockSigner) SignOutputRaw(tx *wire.MsgTx,
+	signDesc *lnwallet.SignDescriptor) ([]byte, error) {
+	amt := signDesc.Output.Value
+	witnessScript := signDesc.WitnessScript
+	privKey := m.key
+
+	sig, err := txscript.RawTxInWitnessSignature(tx, signDesc.SigHashes,
+		signDesc.InputIndex, amt, witnessScript, txscript.SigHashAll, privKey)
+	if err != nil {
+		return nil, err
+	}
+
+	return sig[:len(sig)-1], nil
+}
+func (m *mockSigner) ComputeInputScript(tx *wire.MsgTx,
+	signDesc *lnwallet.SignDescriptor) (*lnwallet.InputScript, error) {
+
+	witnessScript, err := txscript.WitnessScript(tx, signDesc.SigHashes,
+		signDesc.InputIndex, signDesc.Output.Value, signDesc.Output.PkScript,
+		txscript.SigHashAll, m.key, true)
+	if err != nil {
+		return nil, err
+	}
+
+	return &lnwallet.InputScript{
+		Witness: witnessScript,
+	}, nil
+}
+
+type mockNotfier struct {
+	confChannel chan *chainntnfs.TxConfirmation
+}
+
+func (m *mockNotfier) RegisterConfirmationsNtfn(txid *chainhash.Hash, numConfs,
+	heightHint uint32) (*chainntnfs.ConfirmationEvent, error) {
+	return &chainntnfs.ConfirmationEvent{
+		Confirmed: m.confChannel,
+	}, nil
+}
+func (m *mockNotfier) RegisterBlockEpochNtfn() (*chainntnfs.BlockEpochEvent,
+	error) {
+	return nil, nil
+}
+
+func (m *mockNotfier) Start() error {
+	return nil
+}
+
+func (m *mockNotfier) Stop() error {
+	return nil
+}
+func (m *mockNotfier) RegisterSpendNtfn(outpoint *wire.OutPoint,
+	heightHint uint32) (*chainntnfs.SpendEvent, error) {
+	return &chainntnfs.SpendEvent{
+		Spend:  make(chan *chainntnfs.SpendDetail),
+		Cancel: func() {},
+	}, nil
+}
+
+type mockChainIO struct{}
+
+func (m *mockChainIO) GetBestBlock() (*chainhash.Hash, int32, error) {
+	return nil, 0, nil
+}
+
+func (m *mockChainIO) GetUtxo(op *wire.OutPoint,
+	heightHint uint32) (*wire.TxOut, error) {
+	return nil, nil
+}
+
+func (m *mockChainIO) GetBlockHash(blockHeight int64) (*chainhash.Hash, error) {
+	return nil, nil
+}
+
+func (m *mockChainIO) GetBlock(
+	blockHash *chainhash.Hash) (*wire.MsgBlock, error) {
+	return nil, nil
+}
+
+type mockWalletController struct {
+	publTxChan chan *wire.MsgTx
+}
+
+func (m *mockWalletController) FetchInputInfo(
+	prevOut *wire.OutPoint) (*wire.TxOut, error) {
+	return nil, nil
+}
+func (m *mockWalletController) ConfirmedBalance(confs int32,
+	witness bool) (btcutil.Amount, error) {
+	return 0, nil
+}
+func (m *mockWalletController) NewAddress(addrType lnwallet.AddressType,
+	change bool) (btcutil.Address, error) {
+	return nil, nil
+}
+func (m *mockWalletController) GetPrivKey(
+	a btcutil.Address) (*btcec.PrivateKey, error) {
+	return nil, nil
+}
+func (m *mockWalletController) NewRawKey() (*btcec.PublicKey, error) {
+	return nil, nil
+}
+func (m *mockWalletController) FetchRootKey() (*btcec.PrivateKey, error) {
+	return nil, nil
+}
+func (m *mockWalletController) SendOutputs(
+	outputs []*wire.TxOut) (*chainhash.Hash, error) {
+	return nil, nil
+}
+func (m *mockWalletController) ListUnspentWitness(
+	confirms int32) ([]*lnwallet.Utxo, error) {
+	return nil, nil
+}
+func (m *mockWalletController) ListTransactionDetails() ([]*lnwallet.TransactionDetail, error) {
+	return nil, nil
+}
+func (m *mockWalletController) LockOutpoint(o wire.OutPoint) {
+
+}
+func (m *mockWalletController) UnlockOutpoint(o wire.OutPoint) {
+
+}
+func (m *mockWalletController) PublishTransaction(tx *wire.MsgTx) error {
+	m.publTxChan <- tx
+	return nil
+}
+func (m *mockWalletController) SubscribeTransactions() (lnwallet.TransactionSubscription, error) {
+	return nil, nil
+}
+func (m *mockWalletController) IsSynced() (bool, error) {
+	return false, nil
+}
+func (m *mockWalletController) Start() error {
+	return nil
+}
+func (m *mockWalletController) Stop() error {
+	return nil
+}