Merge tag 'pull-nbd-2022-04-26' of https://repo.or.cz/qemu/ericb into staging

nbd patches for 2022-04-26

- Paolo Bonzini: thread-safety improvements to NBD client
- Vladimir Sementsov-Ogievsky: finer-grained selection of bitmaps during
  nbd-export

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* tag 'pull-nbd-2022-04-26' of https://repo.or.cz/qemu/ericb:
  nbd: document what is protected by the CoMutexes
  nbd: take receive_mutex when reading requests[].receiving
  nbd: move s->state under requests_lock
  nbd: code motion and function renaming
  nbd: use a QemuMutex to synchronize yanking, reconnection and coroutines
  nbd: keep send_mutex/free_sema handling outside nbd_co_do_establish_connection
  nbd: remove peppering of nbd_client_connected
  nbd: mark more coroutine_fns
  nbd: safeguard against waking up invalid coroutine
  iotests/223: check new possibility of exporting bitmaps by node/name
  qapi: nbd-export: allow select bitmaps by node/name pair
  qapi: rename BlockDirtyBitmapMergeSource to BlockDirtyBitmapOrStr

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>