smp: Cleanup smp_call_function*()

Get rid of the __call_single_node union and cleanup the API a little
to avoid external code relying on the structure layout as much.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

net/core/dev.c

@@ -11165,8 +11165,7 @@ static int __init net_dev_init(void)
 		INIT_LIST_HEAD(&sd->poll_list);
 		sd->output_queue_tailp = &sd->output_queue;
 #ifdef CONFIG_RPS
-		sd->csd.func = rps_trigger_softirq;
-		sd->csd.info = sd;
+		INIT_CSD(&sd->csd, rps_trigger_softirq, sd);
 		sd->cpu = i;
 #endif