lnwallet: allow callers to specify fee for funding transaction in funding flow

In this commit, we modify the funding reservation workflow slightly to
allow callers to specify their own custom fee when initialization a
funding workflow. This gives power-users the ability to control exactly
how much in fees are paid for each new funding transaction.

lnwallet/reservation.go

@@ -134,7 +134,7 @@ type ChannelReservation struct {
 // used only internally by lnwallet. In order to concurrent safety, the
 // creation of all channel reservations should be carried out via the
 // lnwallet.InitChannelReservation interface.
-func NewChannelReservation(capacity, fundingAmt, feePerKw btcutil.Amount,
+func NewChannelReservation(capacity, fundingAmt, commitFeePerKw btcutil.Amount,
 	wallet *LightningWallet, id uint64, pushMSat lnwire.MilliSatoshi,
 	chainHash *chainhash.Hash) *ChannelReservation {
 
@@ -144,7 +144,9 @@ func NewChannelReservation(capacity, fundingAmt, feePerKw btcutil.Amount,
 		initiator    bool
 	)
 
-	commitFee := btcutil.Amount((int64(feePerKw) * CommitWeight) / 1000)
+	commitFee := btcutil.Amount(
+		(int64(commitFeePerKw) * CommitWeight) / 1000,
+	)
 
 	fundingMSat := lnwire.NewMSatFromSatoshis(fundingAmt)
 	capacityMSat := lnwire.NewMSatFromSatoshis(capacity)
@@ -213,13 +215,13 @@ func NewChannelReservation(capacity, fundingAmt, feePerKw btcutil.Amount,
 			LocalCommitment: channeldb.ChannelCommitment{
 				LocalBalance:  ourBalance,
 				RemoteBalance: theirBalance,
-				FeePerKw:      feePerKw,
+				FeePerKw:      commitFeePerKw,
 				CommitFee:     commitFee,
 			},
 			RemoteCommitment: channeldb.ChannelCommitment{
 				LocalBalance:  ourBalance,
 				RemoteBalance: theirBalance,
-				FeePerKw:      feePerKw,
+				FeePerKw:      commitFeePerKw,
 				CommitFee:     commitFee,
 			},
 			Db: wallet.Cfg.Database,