Merge tag 'next-pull-request' of https://gitlab.com/juan.quintela/qemu into staging

Migration PULL request (take 3)

Hi

Drop everything that is not a bug fix:
- fixes by peter
- fix comment on block creation (me)
- fix return values from qio_channel_block()

Please, apply.

(take 1)
It includes:
- Leonardo fix for zero_copy flush
- Fiona fix for return value of readv/writev
- Peter Xu cleanups
- Peter Xu preempt patches
- Patches ready from zero page (me)
- AVX2 support (ling)
- fix for slow networking and reordering of first packets (manish)

Please, apply.

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# gpg: Good signature from "Juan Quintela <quintela@redhat.com>" [full]
# gpg:                 aka "Juan Quintela <quintela@trasno.org>" [full]
# Primary key fingerprint: 1899 FF8E DEBF 58CC EE03  4B82 F487 EF18 5872 D723

* tag 'next-pull-request' of https://gitlab.com/juan.quintela/qemu:
  migration: Block migration comment or code is wrong
  migration: Disable multifd explicitly with compression
  migration: Use non-atomic ops for clear log bitmap
  migration: Disallow postcopy preempt to be used with compress
  migration: Fix race on qemu_file_shutdown()
  migration: Fix possible infinite loop of ram save process
  migration/multifd/zero-copy: Create helper function for flushing
  migration/channel-block: fix return value for qio_channel_block_{readv,writev}

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>