NFS add support for asynchronous COPY

Change xdr to always send COPY asynchronously.

Keep the list copies send in a list under a server structure.
Once copy is sent, it waits on a completion structure that will
be signalled by the callback thread that receives CB_OFFLOAD.

If CB_OFFLOAD returned an error and even if it returned partial
bytes, ignore them (as we can't commit without a verifier to
match) and return an error.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/linux/nfs_fs.h

@@ -185,6 +185,15 @@ struct nfs_inode {
 	struct inode		vfs_inode;
 };
 
+struct nfs4_copy_state {
+	struct list_head	copies;
+	nfs4_stateid		stateid;
+	struct completion	completion;
+	uint64_t		count;
+	struct nfs_writeverf	verf;
+	int			error;
+};
+
 /*
  * Access bit flags
  */