net/macb: fix race with RX interrupt while doing NAPI

When interrupts are disabled, an RX condition can occur but
it is not reported when enabling interrupts again. We need to check
RSR and use napi_reschedule() if condition is met.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>