ethtool: module: fix cleanup if socket used for flashing multiple devices

ethtool: module: fix cleanup if socket used for flashing multiple devices

When a single Netlink socket issues MODULE_FW_FLASH_ACT against multiple
devices, ethnl_sock_priv_set() overwrites sk_priv->dev on each call,
retaining only the last one. The socket priv is used on socket close,
to walk the global work list and mark the uncompleted flashing work
as "orphaned". Otherwise if another socket reuses the PID it will
unexpectedly receive the flashing notifications.

Don't record the device, record net pointer instead. The purpose of
the dev is to scope the work to a netns, anyway. If we store netns
the overrides are safe/a nop since all flashed devices must be in
the same netns as the socket.

Fixes: 32b4c8b53ee7 ("ethtool: Add ability to flash transceiver modules' firmware")
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Link: https://patch.msgid.link/20260522231312.1710836-6-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>