NFS: Make callbacks minor version generic

I found a few places that hardcode the minor version number rather than
making it dependent on the protocol the callback came in over.  This
patch makes it easier to add new minor versions in the future.

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

fs/nfs/callback.h

@@ -39,6 +39,7 @@ struct cb_process_state {
 	__be32			drc_status;
 	struct nfs_client	*clp;
 	u32			slotid;
+	u32			minorversion;
 	struct net		*net;
 };