net: sgi: ioc3-eth: unregister netdev before freeing DMA rings

ioc3eth_remove() frees the coherent RX and TX descriptor rings before
unregistering the netdev. If the interface is running,
unregister_netdev() invokes ioc3_close() through ndo_stop.

ioc3_close() stops the device and then calls ioc3_free_rx_bufs() and
ioc3_clean_tx_ring(). Both cleanup functions access descriptors in the
rings, so the current ordering causes CPU accesses to freed coherent
memory. Until ioc3_stop() disables RX and TX DMA, the device may also
continue using the freed ring addresses.

Unregister the netdev before releasing the rings. This lets the core
close a running interface and quiesce the device while the rings are
still valid. Keep the explicit timer deletion because ndo_stop is not
called when the interface is already down.

Cc: <stable+noautosel@kernel.org> # untested fix for ancient HW
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Reviewed-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Link: https://patch.msgid.link/40CD736C4911C181+20260629085053.964383-1-raoxu@uniontech.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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