Add virtio_net_id for evenry instance

index a05eafb..66ddfc4 100644
@@ -333,6 +333,7 @@ void *virtio_net_init(PCIBus *bus, NICInfo *nd, int devfn)
 {
     VirtIONet *n;
     const char *info_str = "virtio-net";
+    static int virtio_net_id = 0;
 
     n = (VirtIONet *)virtio_init_pci(bus, info_str, 6900, 0x1000,
 				     0, VIRTIO_ID_NET,

@@ -361,7 +362,7 @@ void *virtio_net_init(PCIBus *bus, NICInfo *nd, int devfn)
              "%s macaddr=%02x:%02x:%02x:%02x:%02x:%02x", info_str,
              nd->macaddr[0], nd->macaddr[1], nd->macaddr[2],
              nd->macaddr[3], nd->macaddr[4], nd->macaddr[5]);
-    register_savevm(info_str, 1, 1, virtio_net_save, virtio_net_load, n);
+    register_savevm(info_str, virtio_net_id++, 1, virtio_net_save, virtio_net_load, n);
 
     return &n->vdev;
 }