net: natsemi: fix rx_dropped double accounting on netif_rx() failure

`netif_rx()` already increments `rx_dropped` core stat when it fails.
The driver was also updating `ndev->stats.rx_dropped` in the same path.
Since both are reported together via `ip -s -s` command, this resulted
in drops being counted twice in user-visible stats.

Keep the driver update on `if (unlikely(!skb))`, but skip it after
`netif_rx()` errors.

Fixes: caf586e ("net: add a core netdev->rx_dropped counter")
Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250913060135.35282-3-yyyynoom@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Cruzer-S

drivers/net/ethernet/natsemi/ns83820.c

@@ -820,7 +820,7 @@ static void rx_irq(struct net_device *ndev)
 	struct ns83820 *dev = PRIV(ndev);
 	struct rx_info *info = &dev->rx_info;
 	unsigned next_rx;
-	int rx_rc, len;
+	int len;
 	u32 cmdsts;
 	__le32 *desc;
 	unsigned long flags;
@@ -881,8 +881,10 @@ static void rx_irq(struct net_device *ndev)
 		if (likely(CMDSTS_OK & cmdsts)) {
 #endif
 			skb_put(skb, len);
-			if (unlikely(!skb))
+			if (unlikely(!skb)) {
+				ndev->stats.rx_dropped++;
 				goto netdev_mangle_me_harder_failed;
+			}
 			if (cmdsts & CMDSTS_DEST_MULTI)
 				ndev->stats.multicast++;
 			ndev->stats.rx_packets++;
@@ -901,15 +903,12 @@ static void rx_irq(struct net_device *ndev)
 				__vlan_hwaccel_put_tag(skb, htons(ETH_P_IPV6), tag);
 			}
 #endif
-			rx_rc = netif_rx(skb);
-			if (NET_RX_DROP == rx_rc) {
-netdev_mangle_me_harder_failed:
-				ndev->stats.rx_dropped++;
-			}
+			netif_rx(skb);
 		} else {
 			dev_kfree_skb_irq(skb);
 		}
 
+netdev_mangle_me_harder_failed:
 		nr++;
 		next_rx = info->next_rx;
 		desc = info->descs + (DESC_SIZE * next_rx);