chainntnfs: make sure notification is sent to the whole set

This commit fixes a bug where the confirmation details may be missed.
When the same tx is subscribed via `RegisterConfirmationsNtfn`, we will
put them into the same set and notify the whole set. However, this logic
is missing when performing the rescan - once the confirmation detail is
found, we only notify the current subscriber. Later we will skip
notifying other subscribers in `UpdateConfDetails` due to the
`confSet.details != nil` check. We now fix it by immediately notify all
the subscribers when the confirmation detail is found during the rescan.

chainntnfs/interface.go

@@ -258,6 +258,9 @@ type ConfirmationEvent struct {
 // channels.
 func NewConfirmationEvent(numConfs uint32, cancel func()) *ConfirmationEvent {
 	return &ConfirmationEvent{
+		// We cannot rely on the subscriber to immediately read from
+		// the channel so we need to create a larger buffer to avoid
+		// blocking the notifier.
 		Confirmed:    make(chan *TxConfirmation, 1),
 		Updates:      make(chan uint32, numConfs),
 		NegativeConf: make(chan int32, 1),