chainntnfs/txnotifier: define ReorgSafetyLimit as 144 blocks

chainntnfs/txnotifier.go

@@ -10,6 +10,15 @@ import (
 	"github.com/btcsuite/btcutil"
 )
 
+const (
+	// ReorgSafetyLimit is the chain depth beyond which it is assumed a
+	// block will not be reorganized out of the chain. This is used to
+	// determine when to prune old confirmation requests so that reorgs are
+	// handled correctly. The average number of blocks in a day is a
+	// reasonable value to use.
+	ReorgSafetyLimit = 144
+)
+
 var (
 	// ErrTxNotifierExiting is an error returned when attempting to interact
 	// with the TxNotifier but it been shut down.