igb: Use an advanced ctx descriptor for launchtime

On i210, Launchtime (TxTime) requires the usage of an "Advanced
Transmit Context Descriptor" for retrieving the timestamp of a packet.

The igb driver correctly builds such descriptor on the segmentation
flow (i.e. igb_tso()) or on the checksum one (i.e. igb_tx_csum()), but the
feature is broken for AF_PACKET if the IGB_TX_FLAGS_VLAN is not set,
which happens due to an early return on igb_tx_csum().

This flag is only set by the kernel when a VLAN interface is used,
thus we can't just rely on it. Here we are fixing this issue by checking
if launchtime is enabled for the current tx_ring before performing the
early return.
Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

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

@@ -5816,7 +5816,8 @@ static void igb_tx_csum(struct igb_ring *tx_ring, struct igb_tx_buffer *first)
 
 	if (skb->ip_summed != CHECKSUM_PARTIAL) {
 csum_failed:
-		if (!(first->tx_flags & IGB_TX_FLAGS_VLAN))
+		if (!(first->tx_flags & IGB_TX_FLAGS_VLAN) &&
+		    !tx_ring->launchtime_enable)
 			return;
 		goto no_csum;
 	}