NFSv4.1: Ensure that layoutget uses the correct gfp modes

Currently, writebacks may end up recursing back into the filesystem due to
GFP_KERNEL direct reclaims in the pnfs subsystem.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/nfs_xdr.h

@@ -233,6 +233,7 @@ struct nfs4_layoutget {
 	struct nfs4_layoutget_args args;
 	struct nfs4_layoutget_res res;
 	struct pnfs_layout_segment **lsegpp;
+	gfp_t gfp_flags;
 };
 
 struct nfs4_getdeviceinfo_args {