sched/headers, timers: Remove the <linux/sysctl.h> include from <linux/timer.h>

So we want to simplify <linux/sched.h>'s header dependencies, but one
roadblock of that is <linux/timer.h>'s inclusion of sysctl.h,
which brings in other, problematic headers.

Note that timer.h's inclusion of sysctl.h can be avoided if we
pre-declare ctl_table - so do that.
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>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/timer.h

@@ -212,7 +212,7 @@ struct hrtimer;
 extern enum hrtimer_restart it_real_fn(struct hrtimer *);
 
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
-#include <linux/sysctl.h>
+struct ctl_table;
 
 extern unsigned int sysctl_timer_migration;
 int timer_migration_handler(struct ctl_table *table, int write,

include/linux/user_namespace.h

@@ -5,6 +5,7 @@
 #include <linux/nsproxy.h>
 #include <linux/ns_common.h>
 #include <linux/sched.h>
+#include <linux/workqueue.h>
 #include <linux/rwsem.h>
 #include <linux/sysctl.h>
 #include <linux/err.h>