nfs: add a helper to set NFS_ODIRECT_RESCHED_WRITES to direct writes

To allow pnfs LD to ask direct writes to be resend.

Signed-off-by: Peng Tao <tao.peng@primarydata.com>
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index ffe4b7a..44e8496 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -502,6 +502,7 @@
 	inode_dio_wait(inode);
 }
 extern ssize_t nfs_dreq_bytes_left(struct nfs_direct_req *dreq);
+extern void nfs_direct_set_resched_writes(struct nfs_direct_req *dreq);
 
 /* nfs4proc.c */
 extern void __nfs4_read_done_cb(struct nfs_pgio_header *);