ext4: disable synchronous transaction batching if max_batch_time==0
The mount manpage says of the max_batch_time option,
This optimization can be turned off entirely
by setting max_batch_time to 0.
But the code doesn't do that. So fix the code to do
Signed-off-by: Eric Sandeen <email@example.com>
Signed-off-by: Theodore Ts'o <firstname.lastname@example.org>