guest can't get ip when create guest with bridge using virtio driver.

[chao zhou]

Environment:
------------
Host OS (ia32/ia32e/IA64):ia32e
Guest OS (ia32/ia32e/IA64):ia32e
Guest OS Type (Linux/Windows):linux
kvm.git Commit:c77dcacb397519b6ade8f08201a4a90a7f4f751e
qemu.git Commit:f2c85a2f36f57f155cda7bc9f7c42b44f1a2439e
Host Kernel Version:3.16.0
Hardware:Ivytown_EP, Haswell_EP

Bug detailed description:
--------------------------
when create guest with bridge, and the bridge network driver is virtio, the guest can not get ip.

note:
1. this is a qemu bug:
kvm + qemu-kvm = result
c77dcacb + f2c85a2f = bad
c77dcacb + 2d591ce2 = good

Reproduce steps:
----------------
1. create guest:
qemu-system-x86_64 -enable-kvm -m 2G -smp 4 -device virtio-net-pci,netdev=net0,mac=00:12:41:34:51:14 -netdev tap,id=net0,script=/etc/kvm/qemu-ifup rhel6u5.qcow

Current result:
----------------
guest can't get ip with bridge using virtio driver.

Expected result:
----------------
guest get ip with bridge using virtio driver.

Basic root-causing log:
----------------------

[chao zhou (chao-zhou)]

kvm.git+ qemu.git:fd275235_8b303011
kernel version:3.17.0_rc1
test on Ivytown_EP
the bug can reproduce

[chao zhou (chao-zhou)]

the first bad commit is
commit cc943c36faa192cd4b32af8fe5edb31894017d35
Author: Jan Kiszka <email address hidden>
Date: Sun Jul 27 09:08:29 2014 +0200

    pci: Use bus master address space for delivering MSI/MSI-X messages

    The spec says (and real HW confirms this) that, if the bus master bit
    is 0, the device will not generate any PCI accesses. MSI and MSI-X
    messages fall among these, so we should use the corresponding address
    space to deliver them. This will prevent delivery if bus master support
    is disabled.

    Cc: <email address hidden>
    Signed-off-by: Jan Kiszka <email address hidden>
    Reviewed-by: Michael S. Tsirkin <email address hidden>
    Signed-off-by: Michael S. Tsirkin <email address hidden>

[chao zhou (chao-zhou)]

kvm.git + qemu.git:da01e614_b6011bd8
test on Ivytown_EP
kernel version: 3.17.0
when create guest with bridge, and the bridge network driver is virtio, the guest can get ip.
the bug cannot reproduce.