Merge remote-tracking branch 'remotes/gkurz/tags/9p-next-2019-10-10' into staging

The most notable change is that we now detect cross-device setups in the
host since it may cause inode number collision and mayhem in the guest.
A new fsdev property is added for the user to choose the appropriate
policy to handle that: either remap all inode numbers or fail I/Os to
another host device or just print out a warning (default behaviour).

This is also my last PR as _active_ maintainer of 9pfs.

# gpg: Signature made Thu 10 Oct 2019 12:14:07 BST
# gpg:                using RSA key B4828BAF943140CEF2A3491071D4D5E5822F73D6
# gpg: Good signature from "Greg Kurz <groug@kaod.org>" [full]
# gpg:                 aka "Gregory Kurz <gregory.kurz@free.fr>" [full]
# gpg:                 aka "[jpeg image of size 3330]" [full]
# Primary key fingerprint: B482 8BAF 9431 40CE F2A3  4910 71D4 D5E5 822F 73D6

* remotes/gkurz/tags/9p-next-2019-10-10:
  MAINTAINERS: Downgrade status of virtio-9p to "Odd Fixes"
  9p: Use variable length suffixes for inode remapping
  9p: stat_to_qid: implement slow path
  9p: Added virtfs option 'multidevs=remap|forbid|warn'
  9p: Treat multiple devices on one export as an error
  fsdev: Add return value to fsdev_throttle_parse_opts()
  9p: Simplify error path of v9fs_device_realize_common()
  9p: unsigned type for type, version, path

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