net: Convert hashlimit_net_ops and recent_net_ops

These pernet_operations just create and destroy /proc entries.
Also, new /proc entries also may come after new nf rules
are added, but this is not possible, when net isn't alive.
So, they are safe to be marked as async.

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