loopdb: store outgoing channel set

Upgrade the database schema to allow for multiple outgoing channels.
This is implemented as an on-the-fly migration leaving the old key in
place.

loopout_test.go

@@ -3,6 +3,7 @@ package loop
 import (
 	"context"
 	"errors"
+	"reflect"
 	"testing"
 	"time"
 
@@ -47,8 +48,11 @@ func TestLoopOutPaymentParameters(t *testing.T) {
 	const maxParts = 5
 
 	// Initiate the swap.
+	req := *testRequest
+	req.OutgoingChanSet = loopdb.ChannelSet{2, 3}
+
 	swap, err := newLoopOutSwap(
-		context.Background(), cfg, height, testRequest,
+		context.Background(), cfg, height, &req,
 	)
 	if err != nil {
 		t.Fatal(err)
@@ -99,6 +103,13 @@ func TestLoopOutPaymentParameters(t *testing.T) {
 			maxParts, swapPayment.MaxParts)
 	}
 
+	// Verify the outgoing channel set restriction.
+	if !reflect.DeepEqual(
+		[]uint64(req.OutgoingChanSet), swapPayment.OutgoingChanIds,
+	) {
+		t.Fatalf("Unexpected outgoing channel set")
+	}
+
 	// Swap is expected to register for confirmation of the htlc. Assert
 	// this to prevent a blocked channel in the mock.
 	ctx.AssertRegisterConf()