igb: Only call skb_tx_timestamp after descriptors are ready

Currently, skb_tx_timestamp() is being called before the Tx
descriptors are prepared in igb_xmit_frame_ring(), which happens
during either the igb_tso() or igb_tx_csum() calls.

Given that now the skb->tstamp might be used to carry the timestamp
for SO_TXTIME, we must only call skb_tx_timestamp() after the
information has been copied into the Tx descriptors.
Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -6033,8 +6033,6 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
 		}
 	}
 
-	skb_tx_timestamp(skb);
-
 	if (skb_vlan_tag_present(skb)) {
 		tx_flags |= IGB_TX_FLAGS_VLAN;
 		tx_flags |= (skb_vlan_tag_get(skb) << IGB_TX_FLAGS_VLAN_SHIFT);
@@ -6050,6 +6048,8 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
 	else if (!tso)
 		igb_tx_csum(tx_ring, first);
 
+	skb_tx_timestamp(skb);
+
 	if (igb_tx_map(tx_ring, first, hdr_len))
 		goto cleanup_tx_tstamp;