arp: Remove a nest in arp_req_get().

This is a prep patch to make the following changes tidy.

No functional change intended.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240430015813.71143-5-kuniyu@amazon.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/arp.c

@@ -1138,23 +1138,28 @@ static int arp_req_get(struct arpreq *r, struct net_device *dev)
 {
 	__be32 ip = ((struct sockaddr_in *) &r->arp_pa)->sin_addr.s_addr;
 	struct neighbour *neigh;
-	int err = -ENXIO;
 
 	neigh = neigh_lookup(&arp_tbl, &ip, dev);
-	if (neigh) {
-		if (!(READ_ONCE(neigh->nud_state) & NUD_NOARP)) {
+	if (!neigh)
+		return -ENXIO;
+
+	if (READ_ONCE(neigh->nud_state) & NUD_NOARP) {
+		neigh_release(neigh);
+		return -ENXIO;
+	}
+
 	read_lock_bh(&neigh->lock);
 	memcpy(r->arp_ha.sa_data, neigh->ha,
 	       min(dev->addr_len, sizeof(r->arp_ha.sa_data_min)));
 	r->arp_flags = arp_state_to_flags(neigh);
 	read_unlock_bh(&neigh->lock);
+
+	neigh_release(neigh);
+
 	r->arp_ha.sa_family = dev->type;
 	strscpy(r->arp_dev, dev->name, sizeof(r->arp_dev));
-			err = 0;
-		}
-		neigh_release(neigh);
-	}
-	return err;
+
+	return 0;
 }
 
 int arp_invalidate(struct net_device *dev, __be32 ip, bool force)