lnd: modify htlc error integration tests to account for max payment size

This commit modifies the HTLC integration tests to be mindful of the
max payment size. Rather than sending the payment in one large batch,
we instead now send it in chunks of the max payment size.

lnd_test.go

@@ -2138,23 +2138,39 @@ out:
 
 	// To do so, we'll push most of the funds in the channel over to
 	// Alice's side, leaving on 10k satoshis of available balance for bob.
-	invoiceReq = &lnrpc.Invoice{
-		Value: int64(chanAmt) - 10000,
-	}
-	carolInvoice2, err := carol.AddInvoice(ctxb, invoiceReq)
-	if err != nil {
-		t.Fatalf("unable to generate carol invoice: %v", err)
-	}
-	if err := bobPayStream.Send(&lnrpc.SendRequest{
-		PaymentRequest: carolInvoice2.PaymentRequest,
-	}); err != nil {
-		t.Fatalf("unable to send payment: %v", err)
-	}
+	// There's a max payment amount, so we'll have to do this
+	// incrementally.
+	amtToSend := int64(chanAmt) - 10000
+	amtSent := int64(0)
+	for amtSent != amtToSend {
+		// We'll send in chunks of the max payment amount. If we're
+		// about to send too much, then we'll only send the amount
+		// remaining.
+		toSend := int64(maxPaymentMSat.ToSatoshis())
+		if toSend+amtSent > amtToSend {
+			toSend = amtToSend - amtSent
+		}
 
-	if resp, err := bobPayStream.Recv(); err != nil {
-		t.Fatalf("payment stream has been closed: %v", err)
-	} else if resp.PaymentError != "" {
-		t.Fatalf("bob's payment failed: %v", err)
+		invoiceReq = &lnrpc.Invoice{
+			Value: toSend,
+		}
+		carolInvoice2, err := carol.AddInvoice(ctxb, invoiceReq)
+		if err != nil {
+			t.Fatalf("unable to generate carol invoice: %v", err)
+		}
+		if err := bobPayStream.Send(&lnrpc.SendRequest{
+			PaymentRequest: carolInvoice2.PaymentRequest,
+		}); err != nil {
+			t.Fatalf("unable to send payment: %v", err)
+		}
+
+		if resp, err := bobPayStream.Recv(); err != nil {
+			t.Fatalf("payment stream has been closed: %v", err)
+		} else if resp.PaymentError != "" {
+			t.Fatalf("bob's payment failed: %v", resp.PaymentError)
+		}
+
+		amtSent += toSend
 	}
 
 	// At this point, Alice has 50mil satoshis on her side of the channel,