Btrfs: Fix split_node to require more empty slots in the node as well

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 8ad8b5c..ac999f0 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1485,7 +1485,7 @@
 		ret = push_nodes_for_insert(trans, root, path, level);
 		c = path->nodes[level];
 		if (!ret && btrfs_header_nritems(c) <
-		    BTRFS_NODEPTRS_PER_BLOCK(root) - 1)
+		    BTRFS_NODEPTRS_PER_BLOCK(root) - 3)
 			return 0;
 		if (ret < 0)
 			return ret;