routing/router: persist payment state machine

This commit makes the router use the ControlTower to drive the payment
life cycle state machine, to keep track of active payments across
restarts.  This lets the router resume payments on startup, such that
their final results can be handled and stored when ready.

routing/router_test.go

@@ -50,6 +50,7 @@ func (c *testCtx) RestartRouter() error {
 		Chain:              c.chain,
 		ChainView:          c.chainView,
 		Payer:              &mockPaymentAttemptDispatcher{},
+		Control:            makeMockControlTower(),
 		ChannelPruneExpiry: time.Hour * 24,
 		GraphPruneInterval: time.Hour * 2,
 	})
@@ -88,6 +89,7 @@ func createTestCtxFromGraphInstance(startingHeight uint32, graphInstance *testGr
 		Chain:              chain,
 		ChainView:          chainView,
 		Payer:              &mockPaymentAttemptDispatcher{},
+		Control:            makeMockControlTower(),
 		ChannelPruneExpiry: time.Hour * 24,
 		GraphPruneInterval: time.Hour * 2,
 		QueryBandwidth: func(e *channeldb.ChannelEdgeInfo) lnwire.MilliSatoshi {
@@ -1528,6 +1530,7 @@ func TestWakeUpOnStaleBranch(t *testing.T) {
 		Chain:              ctx.chain,
 		ChainView:          ctx.chainView,
 		Payer:              &mockPaymentAttemptDispatcher{},
+		Control:            makeMockControlTower(),
 		ChannelPruneExpiry: time.Hour * 24,
 		GraphPruneInterval: time.Hour * 2,
 	})
@@ -2490,3 +2493,30 @@ func assertChannelsPruned(t *testing.T, graph *channeldb.ChannelGraph,
 		}
 	}
 }
+
+type mockControlTower struct{}
+
+var _ channeldb.ControlTower = (*mockControlTower)(nil)
+
+func makeMockControlTower() *mockControlTower {
+	return &mockControlTower{}
+}
+
+func (m *mockControlTower) InitPayment(lntypes.Hash,
+	*channeldb.PaymentCreationInfo) error {
+	return nil
+}
+
+func (m *mockControlTower) RegisterAttempt(lntypes.Hash,
+	*channeldb.PaymentAttemptInfo) error {
+	return nil
+}
+
+func (m *mockControlTower) Success(paymentHash lntypes.Hash,
+	preimg lntypes.Preimage) error {
+	return nil
+}
+
+func (m *mockControlTower) Fail(paymentHash lntypes.Hash) error {
+	return nil
+}