sfc: Fix assignment of ip_summed for pre-allocated skbs

When pre-allocating skbs for received packets, we set ip_summed =
CHECKSUM_UNNCESSARY.  We used to change it back to CHECKSUM_NONE when
the received packet had an incorrect checksum or unhandled protocol.

Commit bc8acf2c ('drivers/net: avoid
some skb->ip_summed initializations') mistakenly replaced the latter
assignment with a DEBUG-only assertion that ip_summed ==
CHECKSUM_NONE.  This assertion is always false, but it seems no-one
has exercised this code path in a DEBUG build.

Fix this by moving our assignment of CHECKSUM_UNNECESSARY into
efx_rx_packet_gro().
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/rx.c

@@ -156,11 +156,10 @@ static int efx_init_rx_buffers_skb(struct efx_rx_queue *rx_queue)
 		if (unlikely(!skb))
 			return -ENOMEM;
 
-		/* Adjust the SKB for padding and checksum */
+		/* Adjust the SKB for padding */
 		skb_reserve(skb, NET_IP_ALIGN);
 		rx_buf->len = skb_len - NET_IP_ALIGN;
 		rx_buf->is_page = false;
-		skb->ip_summed = CHECKSUM_UNNECESSARY;
 
 		rx_buf->dma_addr = pci_map_single(efx->pci_dev,
 						  skb->data, rx_buf->len,
@@ -496,6 +495,7 @@ static void efx_rx_packet_gro(struct efx_channel *channel,
 
 		EFX_BUG_ON_PARANOID(!checksummed);
 		rx_buf->u.skb = NULL;
+		skb->ip_summed = CHECKSUM_UNNECESSARY;
 
 		gro_result = napi_gro_receive(napi, skb);
 	}