r8169: use napi_complete_done return value

Consider the return value of napi_complete_done(), this allows users to
use the gro_flush_timeout sysfs attribute as an alternative to classic
interrupt coalescing.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169_main.c

@@ -4596,10 +4596,8 @@ static int rtl8169_poll(struct napi_struct *napi, int budget)
 
  rtl_tx(dev, tp, budget);
 
- if (work_done < budget) {
- napi_complete_done(napi, work_done);
+ if (work_done < budget && napi_complete_done(napi, work_done))
  rtl_irq_enable(tp);
- }
 
  return work_done;
 }