Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2017-09-25' into staging

nbd patches for 2017-09-25

- Eric Blake: nbd-client: Use correct macro parenthesization
- Vladimir Sementsov-Ogievskiy: 0/3 nbd client refactoring and fixing

# gpg: Signature made Mon 25 Sep 2017 14:39:21 BST
# gpg:                using RSA key 0xA7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>"
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>"
# gpg:                 aka "[jpeg image of size 6874]"
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-nbd-2017-09-25:
  block/nbd-client: nbd_co_send_request: fix return code
  block/nbd-client: simplify check in nbd_co_receive_reply
  block/nbd-client: refactor nbd_co_receive_reply
  nbd-client: Use correct macro parenthesization

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