sched/headers: Prepare to move the task_lock()/unlock() APIs to <linux/sched/task.h>

But first update the code that uses these facilities with the
new header.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

fs/proc/proc_net.c

@@ -17,6 +17,7 @@
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/sched.h>
+#include <linux/sched/task.h>
 #include <linux/module.h>
 #include <linux/bitops.h>
 #include <linux/mount.h>