locks: add a dedicated spinlock to protect i_flctx lists

We can now add a dedicated spinlock without expanding struct inode.
Change to using that to protect the various i_flctx lists.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Acked-by: Christoph Hellwig <hch@lst.de>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ce0873a..32eafa9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -968,6 +968,7 @@
 };
 
 struct file_lock_context {
+	spinlock_t		flc_lock;
 	struct list_head	flc_flock;
 	struct list_head	flc_posix;
 	struct list_head	flc_lease;