uml: simplify helper stack handling

run_helper and run_helper_thread had arguments which were the same in all
callers.  run_helper's stack_out was always NULL and run_helper_thread's
stack_order was always 0.  These are now gone, and the constants folded
into the code.

Also fixed leaks of the helper stack in the AIO and SIGIO code.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/drivers/port_user.c b/arch/um/drivers/port_user.c
index 3f6357d..29250be 100644
--- a/arch/um/drivers/port_user.c
+++ b/arch/um/drivers/port_user.c
@@ -188,7 +188,7 @@
 		{ .sock_fd  		= new,
 		  .pipe_fd 		= socket[1] });
 
-	err = run_helper(port_pre_exec, &data, argv, NULL);
+	err = run_helper(port_pre_exec, &data, argv);
 	if(err < 0)
 		goto out_shutdown;