Merge remote-tracking branch 'remotes/gkurz/tags/9p-next-2020-02-08' into staging

9p patches:
- some more protocol sanity checks
- qtest for readdir
- Christian Schoenebeck now official reviewer

# gpg: Signature made Sat 08 Feb 2020 08:38:10 GMT
# 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-2020-02-08:
  MAINTAINERS: 9pfs: Add myself as reviewer
  tests/virtio-9p: added readdir test
  hw/9pfs/9p-synth: added directory for readdir test
  9pfs: validate count sent by client with T_readdir
  9pfs: require msize >= 4096
  tests/virtio-9p: add terminating null in v9fs_string_read()

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