Merge remote-tracking branch 'remotes/mst/tags/for_upstream' into staging

Merge remote-tracking branch 'remotes/mst/tags/for_upstream' into staging

virtio/vhost: fixes

some bugfixes for virtio/vhost

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
# gpg: Signature made Wed 10 Aug 2016 16:16:22 BST
# gpg:                using RSA key 0x281F0DB8D28D5469
# gpg: Good signature from "Michael S. Tsirkin <mst@kernel.org>"
# gpg:                 aka "Michael S. Tsirkin <mst@redhat.com>"
# Primary key fingerprint: 0270 606B 6F3C DF3D 0B17  0970 C350 3912 AFBE 8E67
#      Subkey fingerprint: 5D09 FD08 71C8 F85B 94CA  8A0D 281F 0DB8 D28D 5469

* remotes/mst/tags/for_upstream:
  vhost-user: Attempt to fix a race with set_mem_table.
  vhost-user: Introduce a new protocol feature REPLY_ACK.
  vhost: check for vhost_ops before using.

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