Schedule the napi after napi_enable() for rx, if it is necessary.

If the rx is completed when napi is disabled, the sheduling of napi
would be lost. Then, no one handles the rx packet until next napi
is scheduled.
Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>