xprtrdma: Add a field of bit flags to struct rpcrdma_req

We have one boolean flag in rpcrdma_req today. I'd like to add more
flags, so convert that boolean to a bit flag.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/xprt_rdma.h

@@ -377,12 +377,17 @@ struct rpcrdma_req {
 	struct rpcrdma_regbuf	*rl_recvbuf;	/* rq_rcv_buf */
 
 	struct list_head	rl_all;
-	bool			rl_backchannel;
+	unsigned long		rl_flags;
 
 	struct list_head	rl_registered;	/* registered segments */
 	struct rpcrdma_mr_seg	rl_segments[RPCRDMA_MAX_SEGS];
 };
 
+/* rl_flags */
+enum {
+	RPCRDMA_REQ_F_BACKCHANNEL = 0,
+};
+
 static inline void
 rpcrdma_set_xprtdata(struct rpc_rqst *rqst, struct rpcrdma_req *req)
 {