[SCTP]: Use inet_ctl_sock_create for control socket creation.

sk->sk_proc->(un)hash is noop right now, so the unification is correct.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>