[ENBD] Doubled requests

[Peter T. Breuer]

"Also sprach Peter T. Breuer:"
> I've run a series of more than a million requests (m_r = 32) and have
> seen no problem with my current code, whereas I was triggering the
> test I gave you before.

Still nothing after 5000000 requests, mixed m_r on and off.

> All I did was set -l and separate the -l and -1 and -0 execution code
> paths in file.c (for debugging).

To fix the wrong default issue, change the codes in file.h to say

 # define NBD_LINEAR_MODE 0
 # define NBD_STRIPE_MODE 1
 # define NBD_MIRROR_MODE 2

(stripe mode was 0 before). Clean. Cook until done.

I'll issue that as a correction.

Peter