tests/qtest/virtio-net: fix hotplug test case

tests/qtest/virtio-net: fix hotplug test case

virtio-net-test has an hotplug testcase that is never executed.

This is because the testcase is attached to virtio-pci interface
rather than to virtio-net-pci.

  $ QTEST_QEMU_BINARY=./qemu-system-x86_64 tests/qtest/qos-test -l | grep hotplug
  /x86_64/.../pci-ohci-tests/ohci_pci-test-hotplug
  /x86_64/.../e1000e/e1000e-tests/hotplug
  /x86_64/.../virtio-blk-pci/virtio-blk-pci-tests/hotplug
  /x86_64/.../vhost-user-blk-pci/vhost-user-blk-pci-tests/hotplug
  /x86_64/.../virtio-rng-pci/virtio-rng-pci-tests/hotplug
  /x86_64/.../virtio-scsi/virtio-scsi-tests/hotplug
  /x86_64/.../virtio-serial/virtio-serial-tests/hotplug

With this fix:

  $ QTEST_QEMU_BINARY=./qemu-system-x86_64 tests/qtest/qos-test -l | grep hotplug
  ...
  /x86_64/.../vhost-user-blk-pci/vhost-user-blk-pci-tests/hotplug
  /x86_64/.../virtio-net-pci/virtio-net-pci-tests/hotplug
  /x86_64/.../virtio-rng-pci/virtio-rng-pci-tests/hotplug
  ...
  $ QTEST_QEMU_BINARY=./qemu-system-x86_64 tests/qtest/qos-test -p /x86_64/.../virtio-net-pci-tests/hotplug
  /x86_64/pc/i440FX-pcihost/pci-bus-pc/pci-bus/virtio-net-pci/virtio-net-pci-tests/hotplug: OK

Fixes: 6ae333f91b99 ("qos-test: virtio-net test node")
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20211028173014.139692-1-lvivier@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>