net: Convert ipvlan_net_ops

net: Convert ipvlan_net_ops

These pernet_operations unregister ipvlan net hooks.
nf_unregister_net_hooks() removes hooks one-by-one,
and then frees the memory via rcu. This looks similar
to that happens, when a new hooks is added: allocation
of bigger memory region, copy of old content, and rcu
freeing the old memory. So, all of net code should be
well with this behavior. Also at the time of hook
unregistering, there are no packets, and foreign net
pernet_operations are not interested in others hooks.
So, we mark them as async.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>