multi: add NewLogClosure in lnutils to avoid repetition

And replaces all usage of `logClosure` with `lnutils.LogClosure`.

discovery/bootstrapper.go

@@ -16,6 +16,7 @@ import (
 	"github.com/btcsuite/btcd/btcutil/bech32"
 	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/autopilot"
+	"github.com/lightningnetwork/lnd/lnutils"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/tor"
 	"github.com/miekg/dns"
@@ -431,7 +432,7 @@ search:
 		}
 
 		log.Tracef("Retrieved SRV records from dns seed: %v",
-			newLogClosure(func() string {
+			lnutils.NewLogClosure(func() string {
 				return spew.Sdump(addrs)
 			}),
 		)