NFS: Create an alloc_client rpc_op

This gives NFS v4 a way to set up callbacks and sessions without v2 or
v3 having to do them as well.

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

fs/nfs/proc.c

@@ -790,6 +790,7 @@ const struct nfs_rpc_ops nfs_v2_clientops = {
 	.close_context	= nfs_close_context,
 	.have_delegation = nfs_have_delegation,
 	.return_delegation = nfs_return_delegation,
+	.alloc_client	= nfs_alloc_client,
 	.init_client	= nfs_init_client,
 	.free_client	= nfs_free_client,
 };