channeldb/migration: copy current lnwire to migration dir

To avoid code changing underneath the static migrations, we copy the
lnwire dependency in its current form into the migration directory.

Ideally the migrations doesn't depend on any code that might change,
this takes us a step closer.

channeldb/migration12/invoices.go

@@ -7,8 +7,8 @@ import (
 	"time"
 
 	"github.com/btcsuite/btcd/wire"
+	lnwire "github.com/lightningnetwork/lnd/channeldb/migration/lnwire21"
 	"github.com/lightningnetwork/lnd/lntypes"
-	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/tlv"
 )
 

channeldb/migration12/migration.go

@@ -4,7 +4,7 @@ import (
 	"bytes"
 
 	"github.com/lightningnetwork/lnd/channeldb/kvdb"
-	"github.com/lightningnetwork/lnd/lnwire"
+	lnwire "github.com/lightningnetwork/lnd/channeldb/migration/lnwire21"
 )
 
 var emptyFeatures = lnwire.NewFeatureVector(nil, nil)