multi: Add decayedlog db migration code

This commit adds the migration code for the decayedlog db which
is optional and will default to true.

channeldb/options.go

@@ -2,6 +2,7 @@ package channeldb
 
 import (
 	"github.com/lightningnetwork/lnd/clock"
+	"github.com/lightningnetwork/lnd/kvdb"
 )
 
 const (
@@ -29,6 +30,14 @@ type OptionalMiragtionConfig struct {
 	// migrations should be run. The index in the array corresponds to the
 	// migration number in optionalVersions.
 	MigrationFlags []bool
+
+	// DecayedLog is a reference to the decayed log database. The channeldb
+	// is inherently part of the optional migration flow so there is no need
+	// to specify it here. The DecayedLog is a separate database in case the
+	// kvdb backend is set to `bbolt`. And also for the kvdb SQL backend
+	// case it is a separate table therefore we need to reference it here
+	// as well to use the right query to access the decayed log.
+	DecayedLog kvdb.Backend
 }
 
 // NewOptionalMiragtionConfig creates a new OptionalMiragtionConfig with the
@@ -136,3 +145,21 @@ func OptionPruneRevocationLog(prune bool) OptionModifier {
 		o.OptionalMiragtionConfig.MigrationFlags[0] = prune
 	}
 }
+
+// OptionWithDecayedLogDB sets the decayed log database reference which might
+// be used for some migrations because generally we only touch the channeldb
+// databases in the migrations, this is a way to allow also access to the
+// decayed log database.
+func OptionWithDecayedLogDB(decayedLog kvdb.Backend) OptionModifier {
+	return func(o *Options) {
+		o.OptionalMiragtionConfig.DecayedLog = decayedLog
+	}
+}
+
+// OptionGcDecayedLog specifies whether the decayed log migration has to
+// take place.
+func OptionGcDecayedLog(noGc bool) OptionModifier {
+	return func(o *Options) {
+		o.OptionalMiragtionConfig.MigrationFlags[1] = !noGc
+	}
+}