[PATCH] migration_thread() race fix

[PATCH] migration_thread() race fix

From: Srivatsa Vaddagiri <vatsa@in.ibm.com>

Noticed that migration_thread can examine "kthread_should_stop()?" without
setting its state to TASK_INTERRUPTIBLE first.  This can cause kthread_stop
on that thread to block forever ...

P.S 	- I assumed that having the task state set to TASK_INTERRUTIBLE
	  while it is doing active_load_balance is fine. It seemed to be
	  the case earlier also.