NFS: add hooks to account for NFSERR_JUKEBOX errors

Make an inode or an nfs_server struct available in the logic that handles
JUKEBOX/DELAY type errors so the NFS client can account for them.

This patch is split out from the main nfs iostat patch to highlight minor
architectural changes required to support this statistic.

Test plan:
None.

Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 77a565e..f1ff4fa 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -51,6 +51,7 @@
 
 #include "nfs4_fs.h"
 #include "delegation.h"
+#include "iostat.h"
 
 #define NFSDBG_FACILITY		NFSDBG_PROC
 
@@ -2755,8 +2756,10 @@
 				rpc_wake_up_task(task);
 			task->tk_status = 0;
 			return -EAGAIN;
-		case -NFS4ERR_GRACE:
 		case -NFS4ERR_DELAY:
+			nfs_inc_server_stats((struct nfs_server *) server,
+						NFSIOS_DELAY);
+		case -NFS4ERR_GRACE:
 			rpc_delay(task, NFS4_POLL_RETRY_MAX);
 			task->tk_status = 0;
 			return -EAGAIN;