ivshmem: Disable irqfd on device reset

ivshmem: Disable irqfd on device reset

The effects of ivshmem_enable_irqfd() was not undone on device reset.

This manifested as:
ivshmem_add_kvm_msi_virq: Assertion `!s->msi_vectors[vector].pdev' failed.

when irqfd was enabled before reset and then enabled again after reset, making
ivshmem_enable_irqfd() run for the second time.

To reproduce, run:

  ivshmem-server

and QEMU with:

  -device ivshmem-doorbell,chardev=iv
  -chardev socket,path=/tmp/ivshmem_socket,id=iv

then install the Windows driver, at the time of writing available at:

https://github.com/virtio-win/kvm-guest-drivers-windows/tree/master/ivshmem

and crash-reboot the guest by inducing a BSOD.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Message-Id: <20171211072110.9058-5-lprosek@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>