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/os-Linux/drivers/ethertap_user.c b/arch/um/os-Linux/drivers/ethertap_user.c
index acba301..cac01b3 100644
--- a/arch/um/os-Linux/drivers/ethertap_user.c
+++ b/arch/um/os-Linux/drivers/ethertap_user.c
@@ -117,7 +117,7 @@
 	pe_data.control_remote = control_remote;
 	pe_data.control_me = control_me;
 	pe_data.data_me = data_me;
-	pid = run_helper(etap_pre_exec, &pe_data, args, NULL);
+	pid = run_helper(etap_pre_exec, &pe_data, args);
 
 	if(pid < 0)
 		err = pid;