sctp: fix a missed .data initialization

As commit 3c68198e("sctp: Make hmac algorithm selection for
 cookie generation dynamic"), we miss the .data initialization.
If we don't use the net_namespace, the problem that parts of the
sysctl configuration won't be isolation and won't occur.

In sctp_sysctl_net_register(), we register the sysctl for each
net, in the for(), we use the 'table[i].data' as check condition, so
when the 'i' is the index of sctp_hmac_alg, the data is NULL, then
break. So add the .data initialization.
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Wang Weidong <wangweidong1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/sysctl.c

@@ -151,6 +151,7 @@ static struct ctl_table sctp_net_table[] = {
 	},
 	{
 		.procname	= "cookie_hmac_alg",
+		.data		= &init_net.sctp.sctp_hmac_alg,
 		.maxlen		= 8,
 		.mode		= 0644,
 		.proc_handler	= proc_sctp_do_hmac_alg,