xfrm: add net device refcount tracker to struct xfrm_state_offload

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Link: https://lore.kernel.org/r/20211209154451.4184050-1-eric.dumazet@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>