datapath: Backport: openvswitch: properly refcount vport-vxlan module

datapath: Backport: openvswitch: properly refcount vport-vxlan module

Upstream commit:
    After 614732eaa12d, 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: 614732eaa12d ("openvswitch: Use regular VXLAN net_device device")
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Upstream: 83e4bf7a74 ("openvswitch: properly refcount vport-vxlan
module").
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Jesse Gross <jesse@kernel.org>