gve: Switch to use napi_complete_done

Use napi_complete_done to allow for the use of gro_flush_timeout.

Fixes: f5cedc84

 ("gve: Add transmit and receive support")
Signed-off-by: Yangchun Fu <yangchun@google.com>
Signed-off-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David Awogbemila <awogbemila@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>