net: Convert ipvs_core_ops

These pernet_operations register and unregister nf hooks,
/proc entries, sysctl, percpu statistics. There are several
global lists, and the only list modified without exclusive
locks is ip_vs_conn_tab in ip_vs_conn_flush(). We iterate
the list and force the timers expire at the moment. Since
there were possible several timer expirations before this
patch, and since they are safe, the patch does not invent
new parallelism of their destruction. These pernet_operations
look safe to be converted.

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