net: drv: netdevsim: don't napi_complete() from netpoll

netdevsim supports netpoll. Make sure we don't call napi_complete()
from it, since it may not be scheduled. Breno reports hitting a
warning in napi_complete_done():

WARNING: CPU: 14 PID: 104 at net/core/dev.c:6592 napi_complete_done+0x2cc/0x560
  __napi_poll+0x2d8/0x3a0
  handle_softirqs+0x1fe/0x710

This is presumably after netpoll stole the SCHED bit prematurely.

Reported-by: Breno Leitao <leitao@debian.org>
Fixes: 3762ec0 ("netdevsim: add NAPI support")
Tested-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20250611174643.2769263-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

drivers/net/netdevsim/netdev.c

@@ -371,7 +371,8 @@ static int nsim_poll(struct napi_struct *napi, int budget)
 	int done;
 
 	done = nsim_rcv(rq, budget);
-	napi_complete(napi);
+	if (done < budget)
+		napi_complete_done(napi, done);
 
 	return done;
 }