nfs41 do not allocate unused back channel pages

Signed-off-by: Andy Adamson <andros@netapp.com>
[Trond.Myklebust@netapp.com: moved definition of svc_is_backchannel()
 into include/linux/sunrpc/bc_xprt.h.]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 538ca43..6dcf8c9 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -506,6 +506,10 @@
 {
 	unsigned int pages, arghi;
 
+	/* bc_xprt uses fore channel allocated buffers */
+	if (svc_is_backchannel(rqstp))
+		return 1;
+
 	pages = size / PAGE_SIZE + 1; /* extra page as we hold both request and reply.
 				       * We assume one is at most one page
 				       */