channeldb: implement compaction

This commit adds the compaction feature of the bbolt compact to our bolt
backend. This will try to open the DB in read-only mode and create a
compacted copy in a temporary file. Once the compaction was successful,
the temporary file and the old source file are swapped atomically.

channeldb/log.go

@@ -3,6 +3,7 @@ package channeldb
 import (
 	"github.com/btcsuite/btclog"
 	"github.com/lightningnetwork/lnd/build"
+	"github.com/lightningnetwork/lnd/channeldb/kvdb"
 	mig "github.com/lightningnetwork/lnd/channeldb/migration"
 	"github.com/lightningnetwork/lnd/channeldb/migration12"
 	"github.com/lightningnetwork/lnd/channeldb/migration13"
@@ -35,4 +36,5 @@ func UseLogger(logger btclog.Logger) {
 	migration12.UseLogger(logger)
 	migration13.UseLogger(logger)
 	migration16.UseLogger(logger)
+	kvdb.UseLogger(logger)
 }