SUNRPC: Add a structure to track multiple transports

In order to support multipathing/trunking we will need the ability to
track multiple transports. This patch sets up a basic structure for
doing so.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

include/linux/sunrpc/xprt.h

@@ -197,6 +197,11 @@ struct rpc_xprt {
 						   transport */
 	unsigned int		bind_index;	/* bind function index */
 
+	/*
+	 * Multipath
+	 */
+	struct list_head	xprt_switch;
+
 	/*
 	 * Connection of transports
 	 */