SUNRPC: minor optimization of "xid" field in rpc_xprt

Move the xid field in the rpc_xprt structure to be in the same cache line
as the reserve_lock, since these are used at the same time.

Test plan:
None.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/xprt.h

@@ -157,11 +157,6 @@ struct rpc_xprt {
 	unsigned char		shutdown   : 1,	/* being shut down */
 				resvport   : 1; /* use a reserved port */
 
-	/*
-	 * XID
-	 */
-	__u32			xid;		/* Next XID value to use */
-
 	/*
 	 * State of TCP reply receive stuff
 	 */
@@ -193,8 +188,8 @@ struct rpc_xprt {
 	 */
 	spinlock_t		transport_lock;	/* lock transport info */
 	spinlock_t		reserve_lock;	/* lock slot table */
+	u32			xid;		/* Next XID value to use */
 	struct rpc_task *	snd_task;	/* Task blocked in send */
-
 	struct list_head	recv;
 
 	struct {