Merge remote-tracking branch 'remotes/jasowang/tags/net-pull-request' into staging

# gpg: Signature made Fri 17 May 2019 10:01:18 BST
# gpg:                using RSA key EF04965B398D6211
# gpg: Good signature from "Jason Wang (Jason Wang on RedHat) <jasowang@redhat.com>" [marginal]
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg:          It is not certain that the signature belongs to the owner.
# Primary key fingerprint: 215D 46F4 8246 689E C77F  3562 EF04 965B 398D 6211

* remotes/jasowang/tags/net-pull-request:
  net/colo-compare.c: Fix a crash in COLO Primary.
  net/slirp: fix the IPv6 prefix length error message
  e1000: Never increment the RX undersize count register
  vhost_net: don't set backend for the uninitialized virtqueue

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