cls_cgroup: remove task_struct parameter from sock_update_classid()

The callers always pass current to sock_update_classid().

Signed-off-by: Li Zefan <lizefan@huawei.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>