sfc: Wrap __efx_rx_packet() with efx_rx_flush_packet()

The pipeline mechanism will need to change a bit for scattered
packets.  Add a wrapper to insulate efx_process_channel() from this.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index 34b56ec..f8013c3 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -250,11 +250,7 @@
 		struct efx_rx_queue *rx_queue =
 			efx_channel_get_rx_queue(channel);
 
-		/* Deliver last RX packet. */
-		if (channel->rx_pkt) {
-			__efx_rx_packet(channel, channel->rx_pkt);
-			channel->rx_pkt = NULL;
-		}
+		efx_rx_flush_packet(channel);
 		if (rx_queue->enabled)
 			efx_fast_push_rx_descriptors(rx_queue);
 	}