nfs41: Backchannel bc_svc_process()

Implement the NFSv4.1 backchannel service.  Invokes the common callback
processing logic svc_process_common() to authenticate the call and
dispatch the appropriate NFSv4.1 XDR decoder and operation procedure.
It then invokes bc_send() to send the reply over the same connection.
bc_send() is implemented in a separate patch.

At this time there is no slot validation or reply cache handling.

[nfs41: Preallocate rpc_rqst receive buffer for handling callbacks]
Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[Move bc_svc_process() declaration to correct patch]
Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 4a8afbd..16043c4 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -419,6 +419,8 @@
 int		   svc_pool_stats_open(struct svc_serv *serv, struct file *file);
 void		   svc_destroy(struct svc_serv *);
 int		   svc_process(struct svc_rqst *);
+int		   bc_svc_process(struct svc_serv *, struct rpc_rqst *,
+			struct svc_rqst *);
 int		   svc_register(const struct svc_serv *, const int,
 				const unsigned short, const unsigned short);