mkfs: factor finobt changes into min log size when formatting

mkfs: factor finobt changes into min log size when formatting

Since the finobt affects the size of the log reservations, we need to
be able to include its effects in the calculation of the minimum log
size.

(Not really a problem now, but adding rmapbt will give this one some
bite.)

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>