sctp: remove the repeat initialize with 0

kmem_cache_zalloc had set the allocated memory to zero. I think no need
to initialize with 0. And move the comments to the function begin.

Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: Wang Weidong <wangweidong1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>