lncfg+itest: expose configurable batch-commit-interval

This will permit a greater degree of tuning or customization depending
on various hardware/environmental factors.

channeldb/options.go

@@ -31,6 +31,10 @@ type Options struct {
 	// channel cache.
 	ChannelCacheSize int
 
+	// BatchCommitInterval is the maximum duration the batch schedulers will
+	// wait before attempting to commit a pending set of updates.
+	BatchCommitInterval time.Duration
+
 	// clock is the time source used by the database.
 	clock clock.Clock
 
@@ -92,6 +96,14 @@ func OptionAutoCompactMinAge(minAge time.Duration) OptionModifier {
 	}
 }
 
+// OptionSetBatchCommitInterval sets the batch commit interval for the internval
+// batch schedulers.
+func OptionSetBatchCommitInterval(interval time.Duration) OptionModifier {
+	return func(o *Options) {
+		o.BatchCommitInterval = interval
+	}
+}
+
 // OptionClock sets a non-default clock dependency.
 func OptionClock(clock clock.Clock) OptionModifier {
 	return func(o *Options) {