Merge remote-tracking branch 'remotes/kraxel/tags/usb-20180612-pull-request' into...

Merge remote-tracking branch 'remotes/kraxel/tags/usb-20180612-pull-request' into staging

usb: bug fix collection, doc update.

# gpg: Signature made Tue 12 Jun 2018 11:44:17 BST
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/usb-20180612-pull-request:
  usb-mtp: Return error on suspicious TYPE_DATA packet from initiator
  usb-hcd-xhci-test: add a test for ccid hotplug
  usb-ccid: fix bus leak
  object: fix OBJ_PROP_LINK_UNREF_ON_RELEASE ambivalence
  bus: do not unref the added child bus on realize
  usb/dev-mtp: Fix use of uninitialized values
  usb: correctly handle Zero Length Packets
  usb: update docs

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