eth: sungem: remove .ndo_poll_controller to avoid deadlocks

Erhard reports netpoll warnings from sungem:

  netpoll_send_skb_on_dev(): eth0 enabled interrupts in poll (gem_start_xmit+0x0/0x398)
  WARNING: CPU: 1 PID: 1 at net/core/netpoll.c:370 netpoll_send_skb+0x1fc/0x20c

gem_poll_controller() disables interrupts, which may sleep.
We can't sleep in netpoll, it has interrupts disabled completely.
Strangely, gem_poll_controller() doesn't even poll the completions,
and instead acts as if an interrupt has fired so it just schedules
NAPI and exits. None of this has been necessary for years, since
netpoll invokes NAPI directly.

Fixes: fe09bb6 ("sungem: Spring cleaning and GRO support")
Reported-and-tested-by: Erhard Furtner <erhard_f@mailbox.org>
Link: https://lore.kernel.org/all/20240428125306.2c3080ef@legion
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240508134504.3560956-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/sun/sungem.c

@@ -949,17 +949,6 @@ static irqreturn_t gem_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
-#ifdef CONFIG_NET_POLL_CONTROLLER
-static void gem_poll_controller(struct net_device *dev)
-{
-	struct gem *gp = netdev_priv(dev);
-
-	disable_irq(gp->pdev->irq);
-	gem_interrupt(gp->pdev->irq, dev);
-	enable_irq(gp->pdev->irq);
-}
-#endif
-
 static void gem_tx_timeout(struct net_device *dev, unsigned int txqueue)
 {
 	struct gem *gp = netdev_priv(dev);
@@ -2839,9 +2828,6 @@ static const struct net_device_ops gem_netdev_ops = {
 	.ndo_change_mtu		= gem_change_mtu,
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_set_mac_address    = gem_set_mac_address,
-#ifdef CONFIG_NET_POLL_CONTROLLER
-	.ndo_poll_controller    = gem_poll_controller,
-#endif
 };
 
 static int gem_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)