htlcswitch/link: add ChannelPoint() to retrieve the channel outpoint.

This function will be used in the switch to retrieve the channel point for a link,
allowing the switch to retrieve individual channels from the database.

htlcswitch/interfaces.go

@@ -1,6 +1,7 @@
 package htlcswitch
 
 import (
+	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lnpeer"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -58,6 +59,9 @@ type ChannelLink interface {
 	// possible).
 	HandleChannelUpdate(lnwire.Message)
 
+	// ChannelPoint returns the channel outpoint for the channel link.
+	ChannelPoint() *wire.OutPoint
+
 	// ChanID returns the channel ID for the channel link. The channel ID
 	// is a more compact representation of a channel's full outpoint.
 	ChanID() lnwire.ChannelID