r6040: call napi_disable when puting down the interface and set lp->dev accordingly.

We did not call napi_disabled when putting down the interface
which should be done. Finally initialize lp->dev when everything
is set.

Signed-off-by: Florian Fainelli <florian.fainelli@telecomint.eu>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>