openvswitch: properly refcount vport-vxlan module

After 614732eaa1, no refcount is maintained for the vport-vxlan module.
This allows the userspace to remove such module while vport-vxlan
devices still exist, which leads to later oops.

v1 -> v2:
 - move vport 'owner' initialization in ovs_vport_ops_register()
   and make such function a macro

Fixes: 614732eaa1 ("openvswitch: Use regular VXLAN net_device device")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/openvswitch/vport-gre.c

@@ -89,7 +89,6 @@ static struct vport_ops ovs_gre_vport_ops = {
 	.create		= gre_create,
 	.send		= dev_queue_xmit,
 	.destroy	= ovs_netdev_tunnel_destroy,
-	.owner		= THIS_MODULE,
 };
 
 static int __init ovs_gre_tnl_init(void)