r8169: prevent potential deadlock in rtl8169_close

r8169: prevent potential deadlock in rtl8169_close

ndo_stop() is RTNL-protected by net core, and the worker function takes
RTNL as well. Therefore we will deadlock when trying to execute a
pending work synchronously. To fix this execute any pending work
asynchronously. This will do no harm because netif_running() is false
in ndo_stop(), and therefore the work function is effectively a no-op.
However we have to ensure that no task is running or pending after
rtl_remove_one(), therefore add a call to cancel_work_sync().

Fixes: abe5fc42f9ce ("r8169: use RTNL to protect critical sections")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/12395867-1d17-4cac-aa7d-c691938fcddf@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>