add sctp_spp_sackdelay_{enable|disable} helper function for
avoiding code duplication.
Signed-off-by: NWang Weidong <wangweidong1@huawei.com>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>