multi: move block epochs dependency from links to switch

In this commit, we move the block height dependency from the links in
the switch to the switch itself. This is possible due to a recent change
on the links no longer depending on the block height to update their
commitment fees.

We'll now only have the switch be alerted of new blocks coming in and
links will retrieve the height from it atomically.

htlcswitch/link.go

@@ -2,17 +2,15 @@ package htlcswitch
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"fmt"
 	prand "math/rand"
 	"sync"
 	"sync/atomic"
 	"time"
 
-	"crypto/sha256"
-
 	"github.com/davecgh/go-spew/spew"
 	"github.com/go-errors/errors"
-	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/contractcourt"
 	"github.com/lightningnetwork/lnd/htlcswitch/hodl"
@@ -213,13 +211,6 @@ type ChannelLinkConfig struct {
 	// transaction to ensure timely confirmation.
 	FeeEstimator lnwallet.FeeEstimator
 
-	// BlockEpochs is an active block epoch event stream backed by an
-	// active ChainNotifier instance. The ChannelLink will use new block
-	// notifications sent over this channel to decide when a _new_ HTLC is
-	// too close to expiry, and also when any active HTLC's have expired
-	// (or are close to expiry).
-	BlockEpochs *chainntnfs.BlockEpochEvent
-
 	// DebugHTLC should be turned on if you want all HTLCs sent to a node
 	// with the debug htlc R-Hash are immediately settled in the next
 	// available state transition.
@@ -290,10 +281,6 @@ type channelLink struct {
 	// method in state machine.
 	batchCounter uint32
 
-	// bestHeight is the best known height of the main chain. The link will
-	// use this information to govern decisions based on HTLC timeouts.
-	bestHeight uint32
-
 	// keystoneBatch represents a volatile list of keystones that must be
 	// written before attempting to sign the next commitment txn. These
 	// represent all the HTLC's forwarded to the link from the switch. Once
@@ -371,8 +358,8 @@ type channelLink struct {
 
 // NewChannelLink creates a new instance of a ChannelLink given a configuration
 // and active channel that will be used to verify/apply updates to.
-func NewChannelLink(cfg ChannelLinkConfig, channel *lnwallet.LightningChannel,
-	currentHeight uint32) ChannelLink {
+func NewChannelLink(cfg ChannelLinkConfig,
+	channel *lnwallet.LightningChannel) ChannelLink {
 
 	return &channelLink{
 		cfg:         cfg,
@@ -381,7 +368,6 @@ func NewChannelLink(cfg ChannelLinkConfig, channel *lnwallet.LightningChannel,
 		// TODO(roasbeef): just do reserve here?
 		logCommitTimer: time.NewTimer(300 * time.Millisecond),
 		overflowQueue:  newPacketQueue(lnwallet.MaxHTLCNumber / 2),
-		bestHeight:     currentHeight,
 		htlcUpdates:    make(chan []channeldb.HTLC),
 		quit:           make(chan struct{}),
 	}
@@ -804,7 +790,6 @@ func (l *channelLink) fwdPkgGarbager() {
 func (l *channelLink) htlcManager() {
 	defer func() {
 		l.wg.Done()
-		l.cfg.BlockEpochs.Cancel()
 		log.Infof("ChannelLink(%v) has exited", l)
 	}()
 
@@ -2095,7 +2080,7 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 			continue
 		}
 
-		heightNow := l.bestHeight
+		heightNow := l.cfg.Switch.BestHeight()
 
 		fwdInfo := chanIterator.ForwardingInstructions()
 		switch fwdInfo.NextHop {