vfs: rename I_MUTEX_QUOTA now that it's not used for quotas

I_MUTEX_QUOTA is now just being used whenever we want to lock two
non-directories.  So the name isn't right.  I_MUTEX_NONDIR2 isn't
especially elegant but it's the best I could think of.

Also fix some outdated documentation.

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/inode.c b/fs/inode.c
index 51f329b..ce48c35 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -957,10 +957,10 @@
 	WARN_ON_ONCE(S_ISDIR(inode2->i_mode));
 	if (inode1 < inode2) {
 		mutex_lock(&inode1->i_mutex);
-		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_QUOTA);
+		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_NONDIR2);
 	} else {
 		mutex_lock(&inode2->i_mutex);
-		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_QUOTA);
+		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_NONDIR2);
 	}
 }
 EXPORT_SYMBOL(lock_two_nondirectories);