SUNRPC: Fix backchannel latency metrics

I noticed that for callback requests, the reported backlog latency
is always zero, and the rtt value is crazy big. The problem was that
rqst->rq_xtime is never set for backchannel requests.

Fixes: 78215759e2 ("SUNRPC: Make RTT measurement more ... ")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/xprtrdma/svc_rdma_backchannel.c

@@ -195,6 +195,7 @@ rpcrdma_bc_send_request(struct svcxprt_rdma *rdma, struct rpc_rqst *rqst)
 	pr_info("%s: %*ph\n", __func__, 64, rqst->rq_buffer);
 #endif
 
+	rqst->rq_xtime = ktime_get();
 	rc = svc_rdma_bc_sendto(rdma, rqst, ctxt);
 	if (rc) {
 		svc_rdma_send_ctxt_put(rdma, ctxt);

net/sunrpc/xprtsock.c

@@ -2660,6 +2660,8 @@ static int bc_sendto(struct rpc_rqst *req)
 		.iov_len	= sizeof(marker),
 	};
 
+	req->rq_xtime = ktime_get();
+
 	len = kernel_sendmsg(transport->sock, &msg, &iov, 1, iov.iov_len);
 	if (len != iov.iov_len)
 		return -EAGAIN;
@@ -2685,7 +2687,6 @@ static int bc_send_request(struct rpc_rqst *req)
 	struct svc_xprt	*xprt;
 	int len;
 
-	dprintk("sending request with xid: %08x\n", ntohl(req->rq_xid));
 	/*
 	 * Get the server socket associated with this callback xprt
 	 */