routing: allow splitting for AMP or MPP

lnrpc/routerrpc/router_backend.go

@@ -696,7 +696,9 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 			payIntent.Amount = *payReq.MilliSat
 		}
 
-		if !payReq.Features.HasFeature(lnwire.MPPOptional) {
+		if !payReq.Features.HasFeature(lnwire.MPPOptional) &&
+			!payReq.Features.HasFeature(lnwire.AMPOptional) {
+
 			payIntent.MaxParts = 1
 		}
 
@@ -765,7 +767,6 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 				ampFeatures := []lnrpc.FeatureBit{
 					lnrpc.FeatureBit_TLV_ONION_OPT,
 					lnrpc.FeatureBit_PAYMENT_ADDR_OPT,
-					lnrpc.FeatureBit_MPP_OPT,
 					lnrpc.FeatureBit_AMP_OPT,
 				}
 

lntest/itest/lnd_amp_test.go

@@ -71,7 +71,6 @@ func testSendPaymentAMP(net *lntest.NetworkHarness, t *harnessTest) {
 			Dest:           net.Bob.PubKey[:],
 			Amt:            int64(paymentAmt),
 			FinalCltvDelta: chainreg.DefaultBitcoinTimeLockDelta,
-			MaxParts:       10,
 			TimeoutSeconds: 60,
 			FeeLimitMsat:   noFeeLimitMsat,
 			Amp:            true,

routing/payment_session.go

@@ -296,9 +296,12 @@ func (p *paymentSession) RequestRoute(maxAmt, feeLimit lnwire.MilliSatoshi,
 				return nil, errNoPathFound
 			}
 
-			if !p.payment.DestFeatures.HasFeature(lnwire.MPPOptional) {
+			destFeatures := p.payment.DestFeatures
+			if !destFeatures.HasFeature(lnwire.MPPOptional) &&
+				!destFeatures.HasFeature(lnwire.AMPOptional) {
+
 				p.log.Debug("not splitting because " +
-					"destination doesn't declare MPP")
+					"destination doesn't declare MPP or AMP")
 
 				return nil, errNoPathFound
 			}