xprtrdma: Eliminate unnecessary lock cycle in xprt_rdma_send_request

The rpcrdma_req is not shared yet, and its associated Send hasn't
been posted, thus RMW should be safe. There's no need for the
expense of a lock cycle here.

Fixes: 0ba6f370 ("xprtrdma: Refactor rpcrdma_deferred_completion")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/transport.c

@@ -735,7 +735,7 @@ xprt_rdma_send_request(struct rpc_task *task)
 		goto drop_connection;
 	req->rl_connect_cookie = xprt->connect_cookie;
 
-	set_bit(RPCRDMA_REQ_F_PENDING, &req->rl_flags);
+	__set_bit(RPCRDMA_REQ_F_PENDING, &req->rl_flags);
 	if (rpcrdma_ep_post(&r_xprt->rx_ia, &r_xprt->rx_ep, req))
 		goto drop_connection;