Doc update: Correct magic values from nbd protocol, V2

The magic number documentation refers to old values for
NBD_REQUEST_MAGIC and NBD_REPLY_MAGIC: The documented values were used
until Linux 2.1.116pre2.

Thus:
- Update the documentation.
- Update the header file: The authorative source for the nbd protocol
  is proto.md from the nbd package, thus mention this.
- Remove the historic values from the header file.
  The historic values are still documented in proto.md from the nbd
  package.

Removing the historic values is intentional:
The values are stale for > 20 years, and this was not noticed.
My guess is that everyone used grep to confirm that the values are
still in use - and the historic values resulted that there were
still hits with grep, ...

Signed-off-by: Manfred Spraul <manfred.spraul@de.bosch.com>
Link: https://github.com/NetworkBlockDevice/nbd/commit/107356ee528eb30744d518a8ac1cb6d379da4868
Link: https://lore.kernel.org/all/20220318200446.14648-1-manfred@colorfullife.com/
Link: https://lists.debian.org/nbd/2022/01/msg00039.html
Link: https://lore.kernel.org/r/20220805082532.55131-1-manfred@colorfullife.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/uapi/linux/nbd.h b/include/uapi/linux/nbd.h
index 20d6cc91435d..88752b20e6c8 100644
--- a/include/uapi/linux/nbd.h
+++ b/include/uapi/linux/nbd.h
@@ -11,6 +11,8 @@
  *            Cleanup PARANOIA usage & code.
  * 2004/02/19 Paul Clements
  *            Removed PARANOIA, plus various cleanup and comments
+ *
+ * See doc/proto.md of the nbd package for more details on the protocol.
  */
 
 #ifndef _UAPILINUX_NBD_H
@@ -63,7 +65,6 @@ enum {
 
 #define NBD_REQUEST_MAGIC 0x25609513
 #define NBD_REPLY_MAGIC 0x67446698
-/* Do *not* use magics: 0x12560953 0x96744668. */
 
 /*
  * This is the packet used for communication between client and