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 <[e-mail]>
Signed-off-by: Anna Schumaker <[e-mail]>

net/sunrpc/xprtrdma/backchannel.c

···
 	req = rpcrdma_create_req(r_xprt);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
-	req->rl_backchannel = true;
+	__set_bit(RPCRDMA_REQ_F_BACKCHANNEL, &req->rl_flags);
 
 	rb = rpcrdma_alloc_regbuf(RPCRDMA_HDRBUF_SIZE,
 				  DMA_TO_DEVICE, GFP_KERNEL);

net/sunrpc/xprtrdma/transport.c

···
 	struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
 	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
 
-	if (req->rl_backchannel)
+	if (test_bit(RPCRDMA_REQ_F_BACKCHANNEL, &req->rl_flags))
 		return;
 
 	dprintk("RPC:       %s: called on 0x%p\n", __func__, req->rl_reply);

net/sunrpc/xprtrdma/verbs.c

···
 			rc = PTR_ERR(req);
 			goto out;
 		}
-		req->rl_backchannel = false;
 		list_add(&req->rl_list, &buf->rb_send_bufs);
 	}
 

net/sunrpc/xprtrdma/xprt_rdma.h

···
 	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