sunvnet: Reset LDC_EVENT_DATA_READY when napi completes.

When vnet_event_napi re-enables interrupts, it should
reset LDC_EVENT_DATA_READY as an optimization.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>