virtio: set pci bus master enable bit

As all virtio devices perform DMA, we
must enable bus mastering for them to be
spec compliant.

This patch fixes hotplug of virtio devices
with Linux guests and qemu 0.11-0.12.
Tested-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_pci.c

@@ -649,6 +649,7 @@ static int __devinit virtio_pci_probe(struct pci_dev *pci_dev,
 		goto out_req_regions;
 
 	pci_set_drvdata(pci_dev, vp_dev);
+	pci_set_master(pci_dev);
 
 	/* we use the subsystem vendor/device id as the virtio vendor/device
 	 * id.  this allows us to use the same PCI vendor/device id for all