multi: move DBMPPayment to paymentsdb package

diff --git a/payments/db/interface.go b/payments/db/interface.go
index 9b91de9..c41dc37 100644
--- a/payments/db/interface.go
+++ b/payments/db/interface.go
@@ -89,3 +89,35 @@ type PaymentControl interface {
 	// completed, and the payment has reached a final terminal state.
 	DeleteFailedAttempts(lntypes.Hash) error
 }
+
+// DBMPPayment is an interface that represents the payment state during a
+// payment lifecycle.
+type DBMPPayment interface {
+	// GetState returns the current state of the payment.
+	GetState() *MPPaymentState
+
+	// Terminated returns true if the payment is in a final state.
+	Terminated() bool
+
+	// GetStatus returns the current status of the payment.
+	GetStatus() PaymentStatus
+
+	// NeedWaitAttempts specifies whether the payment needs to wait for the
+	// outcome of an attempt.
+	NeedWaitAttempts() (bool, error)
+
+	// GetHTLCs returns all HTLCs of this payment.
+	GetHTLCs() []HTLCAttempt
+
+	// InFlightHTLCs returns all HTLCs that are in flight.
+	InFlightHTLCs() []HTLCAttempt
+
+	// AllowMoreAttempts is used to decide whether we can safely attempt
+	// more HTLCs for a given payment state. Return an error if the payment
+	// is in an unexpected state.
+	AllowMoreAttempts() (bool, error)
+
+	// TerminalInfo returns the settled HTLC attempt or the payment's
+	// failure reason.
+	TerminalInfo() (*HTLCAttempt, *FailureReason)
+}
diff --git a/routing/control_tower.go b/routing/control_tower.go
index fcbfbe8..c5d91e8 100644
--- a/routing/control_tower.go
+++ b/routing/control_tower.go
@@ -9,38 +9,6 @@ import (
 	"github.com/lightningnetwork/lnd/queue"
 )
 
-// DBMPPayment is an interface derived from channeldb.MPPayment that is used by
-// the payment lifecycle.
-type DBMPPayment interface {
-	// GetState returns the current state of the payment.
-	GetState() *paymentsdb.MPPaymentState
-
-	// Terminated returns true if the payment is in a final state.
-	Terminated() bool
-
-	// GetStatus returns the current status of the payment.
-	GetStatus() paymentsdb.PaymentStatus
-
-	// NeedWaitAttempts specifies whether the payment needs to wait for the
-	// outcome of an attempt.
-	NeedWaitAttempts() (bool, error)
-
-	// GetHTLCs returns all HTLCs of this payment.
-	GetHTLCs() []paymentsdb.HTLCAttempt
-
-	// InFlightHTLCs returns all HTLCs that are in flight.
-	InFlightHTLCs() []paymentsdb.HTLCAttempt
-
-	// AllowMoreAttempts is used to decide whether we can safely attempt
-	// more HTLCs for a given payment state. Return an error if the payment
-	// is in an unexpected state.
-	AllowMoreAttempts() (bool, error)
-
-	// TerminalInfo returns the settled HTLC attempt or the payment's
-	// failure reason.
-	TerminalInfo() (*paymentsdb.HTLCAttempt, *paymentsdb.FailureReason)
-}
-
 // ControlTower tracks all outgoing payments made, whose primary purpose is to
 // prevent duplicate payments to the same payment hash. In production, a
 // persistent implementation is preferred so that tracking can survive across
@@ -76,7 +44,7 @@ type ControlTower interface {
 
 	// FetchPayment fetches the payment corresponding to the given payment
 	// hash.
-	FetchPayment(paymentHash lntypes.Hash) (DBMPPayment, error)
+	FetchPayment(paymentHash lntypes.Hash) (paymentsdb.DBMPPayment, error)
 
 	// FailPayment transitions a payment into the Failed state, and records
 	// the ultimate reason the payment failed. Note that this should only
@@ -273,7 +241,7 @@ func (p *controlTower) FailAttempt(paymentHash lntypes.Hash,
 
 // FetchPayment fetches the payment corresponding to the given payment hash.
 func (p *controlTower) FetchPayment(paymentHash lntypes.Hash) (
-	DBMPPayment, error) {
+	paymentsdb.DBMPPayment, error) {
 
 	return p.db.FetchPayment(paymentHash)
 }
diff --git a/routing/mock_test.go b/routing/mock_test.go
index 9cb938f..19a76ee 100644
--- a/routing/mock_test.go
+++ b/routing/mock_test.go
@@ -510,7 +510,7 @@ func (m *mockControlTowerOld) FailPayment(phash lntypes.Hash,
 }
 
 func (m *mockControlTowerOld) FetchPayment(phash lntypes.Hash) (
-	DBMPPayment, error) {
+	paymentsdb.DBMPPayment, error) {
 
 	m.Lock()
 	defer m.Unlock()
@@ -787,7 +787,7 @@ func (m *mockControlTower) FailPayment(phash lntypes.Hash,
 }
 
 func (m *mockControlTower) FetchPayment(phash lntypes.Hash) (
-	DBMPPayment, error) {
+	paymentsdb.DBMPPayment, error) {
 
 	args := m.Called(phash)
 
@@ -825,7 +825,7 @@ type mockMPPayment struct {
 	mock.Mock
 }
 
-var _ DBMPPayment = (*mockMPPayment)(nil)
+var _ paymentsdb.DBMPPayment = (*mockMPPayment)(nil)
 
 func (m *mockMPPayment) GetState() *paymentsdb.MPPaymentState {
 	args := m.Called()
diff --git a/routing/payment_lifecycle.go b/routing/payment_lifecycle.go
index 245e3b3..cc92a8b 100644
--- a/routing/payment_lifecycle.go
+++ b/routing/payment_lifecycle.go
@@ -130,7 +130,7 @@ const (
 // wait for results, the method will exit with `stepExit` such that the payment
 // lifecycle loop will terminate.
 func (p *paymentLifecycle) decideNextStep(
-	payment DBMPPayment) (stateStep, error) {
+	payment paymentsdb.DBMPPayment) (stateStep, error) {
 
 	// Check whether we could make new HTLC attempts.
 	allow, err := payment.AllowMoreAttempts()
@@ -1110,7 +1110,9 @@ func (p *paymentLifecycle) patchLegacyPaymentHash(
 // reloadInflightAttempts is called when the payment lifecycle is resumed after
 // a restart. It reloads all inflight attempts from the control tower and
 // collects the results of the attempts that have been sent before.
-func (p *paymentLifecycle) reloadInflightAttempts() (DBMPPayment, error) {
+func (p *paymentLifecycle) reloadInflightAttempts() (paymentsdb.DBMPPayment,
+	error) {
+
 	payment, err := p.router.cfg.Control.FetchPayment(p.identifier)
 	if err != nil {
 		return nil, err
@@ -1133,7 +1135,7 @@ func (p *paymentLifecycle) reloadInflightAttempts() (DBMPPayment, error) {
 }
 
 // reloadPayment returns the latest payment found in the db (control tower).
-func (p *paymentLifecycle) reloadPayment() (DBMPPayment,
+func (p *paymentLifecycle) reloadPayment() (paymentsdb.DBMPPayment,
 	*paymentsdb.MPPaymentState, error) {
 
 	// Read the db to get the latest state of the payment.