drivers: net: xgene: Fix regression in CRC stripping

All packets on ingress (except for jumbo) are terminated with a 4-bytes
CRC checksum. It's the responsability of the driver to strip those 4
bytes. Unfortunately a change dating back to March 2017 re-shuffled some
code and made the CRC stripping code effectively dead.

This change re-orders that part a bit such that the datalen is
immediately altered if needed.

Fixes: 4902a92270fb ("drivers: net: xgene: Add workaround for errata 10GE_8/ENET_11")
Cc: [e-mail]
Signed-off-by: Stephane Graber <[e-mail]>
Tested-by: Stephane Graber <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/apm/xgene/xgene_enet_main.c

···
 	buf_pool->rx_skb[skb_index] = NULL;
 
 	datalen = xgene_enet_get_data_len(le64_to_cpu(raw_desc->m1));
+
+	/* strip off CRC as HW isn't doing this */
+	nv = GET_VAL(NV, le64_to_cpu(raw_desc->m0));
+	if (!nv)
+		datalen -= 4;
+
 	skb_put(skb, datalen);
 	prefetch(skb->data - NET_IP_ALIGN);
 	skb->protocol = eth_type_trans(skb, ndev);
···
 		}
 	}
 
-	nv = GET_VAL(NV, le64_to_cpu(raw_desc->m0));
-	if (!nv) {
-		/* strip off CRC as HW isn't doing this */
-		datalen -= 4;
+	if (!nv)
 		goto skip_jumbo;
-	}
 
 	slots = page_pool->slots - 1;
 	head = page_pool->head;