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>
diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 377a616..96d5f81 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -886,6 +886,7 @@ struct nfs_server *nfs_alloc_server(void)
 	INIT_LIST_HEAD(&server->delegations);
 	INIT_LIST_HEAD(&server->layouts);
 	INIT_LIST_HEAD(&server->state_owners_lru);
+	INIT_LIST_HEAD(&server->ss_copies);
 
 	atomic_set(&server->active, 0);