ethoc: Double check pending RX packet

An interrupt may occur between checking bd.stat and clearing the
interrupt source register which would result in the packet going totally
unnoticed as the interrupt will be missed.  Double check bd.stat after
clearing the interrupt source register to guard against such an
occurrence.

Signed-off-by: Jonas Bonn <jonas@southpole.se>
Signed-off-by: David S. Miller <davem@davemloft.net>