rpc: move sk_bc_xprt to svc_xprt

This seems obviously transport-level information even if it's currently
used only by the server socket code.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index c8f81da..7ad9751 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -79,6 +79,7 @@
 	struct list_head	xpt_users;	/* callbacks on free */
 
 	struct net		*xpt_net;
+	struct rpc_xprt		*xpt_bc_xprt;	/* NFSv4.1 backchannel */
 };
 
 static inline void unregister_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)