After unregister_netdevice() call the request is queued and
reg_state is changed to NETREG_UNREGISTERING.
As we check for NETREG_UNREGISTERED state, free_netdev() never
gets executed causing memory leak.
Initialize "dev->destructor" to free_netdev() to free device
data after unregistration.
Cc: <stable@vger.kernel.org> Reported-by: Daniel Drake <dsd@laptop.org> Tested-by: Daniel Drake <dsd@laptop.org> Signed-off-by: Amitkumar Karwar <akarwar@marvell.com> Signed-off-by: Bing Zhao <bzhao@marvell.com> Signed-off-by: John W. Linville <linville@tuxdriver.com>