net: Convert sctp_defaults_ops

These pernet_operations have a deal with sysctl, /proc
entries and statistics. Also, there are freeing of
net::sctp::addr_waitq queue and net::sctp::local_addr_list
in exit method. All of them look pernet-divided, and it
seems these items are only interesting for sctp_defaults_ops,
which are safe to be executed in parallel.

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