* remotes/bonzini/nbd-next:
nbd: Handle NBD_OPT_LIST option.
nbd: Handle fixed new-style clients.
nbd: Shutdown socket before closing.
nbd: Don't validate from and len in NBD_CMD_DISC.
nbd: Don't export a block device with no medium.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>