Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2022-01-28' into staging

nbd patches for 2022-01-28

- Hanna Reitz: regression fix for block status caching
- Philippe Mathieu-Daude: documentation formatting
- Nir Soffer: dead code removal

# gpg: Signature made Fri 28 Jan 2022 22:58:50 GMT
# gpg:                using RSA key 71C2CC22B1C4602927D2F3AAA7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>" [full]
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>" [full]
# gpg:                 aka "[jpeg image of size 6874]" [full]
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-nbd-2022-01-28:
  iotests/block-status-cache: New test
  block/io: Update BSC only if want_zero is true
  qapi/block: Cosmetic change in BlockExportType schema
  nbd/server.c: Remove unused field

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>