xfrm: handle NETDEV_UNREGISTER for xfrm device

xfrm: handle NETDEV_UNREGISTER for xfrm device

commit df23aa422ae6d147cc088030677d3250cdb24dc4 upstream.

This patch to handle the asynchronous unregister
device event so the device IPsec offload resources
could be cleanly released.

Fixes: cdf6302c04af ("xfrm: policy: remove pcpu policy cache")
Signed-off-by: Raed Salem <raeds@mellanox.com>
Reviewed-by: Boris Pismenny <borisp@mellanox.com>
Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>