NFS: Don't revalidate the file on close if we hold a delegation

If we're holding a delegation, we can skip sending the close-to-open
GETATTR until we're returning that delegation.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 7de345f..2fc237c 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -795,6 +795,8 @@
 	if (!is_sync)
 		return;
 	inode = d_inode(ctx->dentry);
+	if (NFS_PROTO(inode)->have_delegation(inode, FMODE_READ))
+		return;
 	nfsi = NFS_I(inode);
 	if (inode->i_mapping->nrpages == 0)
 		return;