routing: distinguish between receiver amount and total amount in newRoute

routing/pathfind.go

@@ -74,6 +74,7 @@ type edgePolicyWithSource struct {
 // custom records and payment address.
 type finalHopParams struct {
 	amt         lnwire.MilliSatoshi
+	totalAmt    lnwire.MilliSatoshi
 	cltvDelta   uint16
 	records     record.CustomSet
 	paymentAddr *[32]byte
@@ -177,7 +178,8 @@ func newRoute(sourceVertex route.Vertex,
 			// Otherwise attach the mpp record if it exists.
 			if finalHop.paymentAddr != nil {
 				mpp = record.NewMPP(
-					finalHop.amt, *finalHop.paymentAddr,
+					finalHop.totalAmt,
+					*finalHop.paymentAddr,
 				)
 			}
 		} else {

routing/pathfind_test.go

@@ -1327,6 +1327,7 @@ func TestNewRoute(t *testing.T) {
 				sourceVertex, testCase.hops, startingHeight,
 				finalHopParams{
 					amt:         testCase.paymentAmount,
+					totalAmt:    testCase.paymentAmount,
 					cltvDelta:   finalHopCLTV,
 					records:     nil,
 					paymentAddr: testCase.paymentAddr,

routing/payment_session.go

@@ -196,6 +196,7 @@ func (p *paymentSession) RequestRoute(maxAmt, feeLimit lnwire.MilliSatoshi,
 		sourceVertex, path, height,
 		finalHopParams{
 			amt:         maxAmt,
+			totalAmt:    maxAmt,
 			cltvDelta:   finalCltvDelta,
 			records:     p.payment.DestCustomRecords,
 			paymentAddr: p.payment.PaymentAddr,

routing/router.go

@@ -1456,6 +1456,7 @@ func (r *ChannelRouter) FindRoute(source, target route.Vertex,
 		source, path, uint32(currentHeight),
 		finalHopParams{
 			amt:       amt,
+			totalAmt:  amt,
 			cltvDelta: finalExpiry,
 			records:   destCustomRecords,
 		},
@@ -2513,6 +2514,7 @@ func (r *ChannelRouter) BuildRoute(amt *lnwire.MilliSatoshi,
 		source, pathEdges, uint32(height),
 		finalHopParams{
 			amt:       receiverAmt,
+			totalAmt:  receiverAmt,
 			cltvDelta: uint16(finalCltvDelta),
 			records:   nil,
 		},