cgroup: consolidate cgroup_attach_task() and cgroup_attach_proc()

These two functions share most of the code.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index efbfca7..98d458a 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2008,7 +2008,7 @@
 	struct cgroup *new_cgroup = scan->data;
 
 	cgroup_lock();
-	cgroup_attach_task(new_cgroup, tsk);
+	cgroup_attach_task(new_cgroup, tsk, false);
 	cgroup_unlock();
 }