server+routing: pass isAlias to router

This allows the router to determine what is and isn't an alias from
lnd's definition of an alias. Any ChannelAnnouncement that has an
alias ShortChannelID field is not verified on-chain. To prevent a
DoS vector from existing, the gossiper ensures that only the local
lnd node can send its ChannelAnnouncements to the router with an
alias ShortChannelID.

routing/payment_lifecycle_test.go

@@ -473,6 +473,9 @@ func testPaymentLifecycle(t *testing.T, test paymentLifecycleTestCase,
 				return next, nil
 			},
 			Clock: clock.NewTestClock(time.Unix(1, 0)),
+			IsAlias: func(scid lnwire.ShortChannelID) bool {
+				return false
+			},
 		})
 		if err != nil {
 			t.Fatalf("unable to create router %v", err)