CVE-2024-38597 eth: sungem: remove .ndo_poll_controller to avoid deadlocks

In the Linux kernel, the following vulnerability has been resolved:

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.