lncfg: increase DefaultIncomingBroadcastDelta to 16

With this change, we'll go to chain even earlier to ensure that we have
enough time to sweep a potentially contested HTLC, now that we're
waiting longer before sweeps to ensure that the commitment transaction
is sufficeitnyl burried before we sweep.

lncfg/config.go

@@ -20,11 +20,16 @@ const (
 	// DefaultIncomingBroadcastDelta defines the number of blocks before the
 	// expiry of an incoming htlc at which we force close the channel. We
 	// only go to chain if we also have the preimage to actually pull in the
-	// htlc. BOLT #2 suggests 7 blocks. We use a few more for extra safety.
-	// Within this window we need to get our sweep or 2nd level success tx
-	// confirmed, because after that the remote party is also able to claim
-	// the htlc using the timeout path.
-	DefaultIncomingBroadcastDelta = 10
+	// htlc. BOLT #2 suggests 7 blocks. We use more for extra safety.
+	//
+	// The value accounts for:
+	//   - Up to 6 blocks waiting for close tx confirmation (reorg safety)
+	//   - Time to broadcast and confirm our sweep/2nd level success tx
+	//
+	// Within this window we need to get our sweep confirmed, because after
+	// that the remote party is also able to claim the htlc using the
+	// timeout path.
+	DefaultIncomingBroadcastDelta = 16
 
 	// DefaultFinalCltvRejectDelta defines the number of blocks before the
 	// expiry of an incoming exit hop htlc at which we cancel it back