Merge remote-tracking branch 'bonzini/nbd-for-anthony' into staging

Merge remote-tracking branch 'bonzini/nbd-for-anthony' into staging

* bonzini/nbd-for-anthony: (26 commits)
  nbd: add myself as maintainer
  qemu-nbd: throttle requests
  qemu-nbd: asynchronous operation
  qemu-nbd: add client pointer to NBDRequest
  qemu-nbd: move client handling to nbd.c
  qemu-nbd: use common main loop
  link the main loop and its dependencies into the tools
  qemu-nbd: introduce NBDRequest
  qemu-nbd: introduce NBDExport
  qemu-nbd: introduce nbd_do_receive_request
  qemu-nbd: more robust handling of invalid requests
  qemu-nbd: introduce nbd_do_send_reply
  qemu-nbd: simplify nbd_trip
  move corking functions to osdep.c
  qemu-nbd: remove data_size argument to nbd_trip
  qemu-nbd: remove offset argument to nbd_trip
  Update ioctl order in nbd_init() to detect EBUSY
  nbd: add support for NBD_CMD_TRIM
  nbd: add support for NBD_CMD_FLUSH
  nbd: add support for NBD_CMD_FLAG_FUA
  ...