procfs: report EISDIR when reading sysctl dirs in proc

On reading sysctl dirs we should return -EISDIR instead of -EINVAL.
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/proc_sysctl.c

@@ -370,6 +370,7 @@ static const struct file_operations proc_sys_file_operations = {
 };
 
 static const struct file_operations proc_sys_dir_file_operations = {
+	.read		= generic_read_dir,
 	.readdir	= proc_sys_readdir,
 	.llseek		= generic_file_llseek,
 };