net: Convert cangw_pernet_ops

These pernet_operations have a deal with cgw_list,
and the rest of accesses are made under rtnl_lock().
The only exception is cgw_dump_jobs(), which is
accessed under rcu_read_lock(). cgw_dump_jobs() is
called on netlink request, and it does not seem,
foreign pernet_operations want to send a net such
the messages. So, we mark them as async.

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