Merge tag 'pull-nbd-2023-09-25' of https://repo.or.cz/qemu/ericb into staging

NBD patches through 2023-09-25

- Denis V. Lunev: iotest improvements
- Eric Blake: further work towards 64-bit NBD extensions

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* tag 'pull-nbd-2023-09-25' of https://repo.or.cz/qemu/ericb:
  nbd/server: Refactor handling of command sanity checks
  nbd: Prepare for 64-bit request effect lengths
  nbd: Add types for extended headers
  nbd/client: Pass mode through to nbd_send_request
  nbd: Replace bool structured_reply with mode enum
  iotests: improve 'not run' message for nbd-multiconn test
  iotests: use TEST_IMG_FILE instead of TEST_IMG in _require_large_file

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>