r8169: fix lockdep warning when removing interface

The work queue is initialised in rtl_open (when the interface goes up),
but canceled in rtl_remove_one (when the PCI device gets removed). If
the network interface is not brought up, then the work queue struct is
not initialised. When the device is removed, the attempt to cancel the
uninitialised work queue causes a lockdep warning.

This patch fixes the issue by moving cancel_work_sync to rtl_close (to
match rtl_open). (Note that rtl_close is also called via
unregister_netdev in rtl_remove_one.)

Signed-off-by: Peter Wu <lekensteyn@gmail.com>
Acked-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>