routing: process successes in mission control

This commit modifies paymentLifecycle so that it not only feeds
failures into mission control, but successes as well.
This allows for more accurate probability estimates. Previously,
the success probability for a successful pair and a pair with
no history was equal. There was no force that pushed towards
previously successful routes.

routing/payment_lifecycle.go

@@ -161,6 +161,15 @@ func (p *paymentLifecycle) resumePayment() ([32]byte, *route.Route, error) {
 		log.Debugf("Payment %x succeeded with pid=%v",
 			p.payment.PaymentHash, p.attempt.PaymentID)
 
+		// Report success to mission control.
+		err = p.router.cfg.MissionControl.ReportPaymentSuccess(
+			p.attempt.PaymentID, &p.attempt.Route,
+		)
+		if err != nil {
+			log.Errorf("Error reporting payment success to mc: %v",
+				err)
+		}
+
 		// In case of success we atomically store the db payment and
 		// move the payment to the success state.
 		err = p.router.cfg.Control.Success(p.payment.PaymentHash, result.Preimage)