net/mlx5e: FPGA, fix Innova IPsec TX offload data path performance

At Innova IPsec TX offload data path a special software parser metadata
is used to pass some packet attributes to the hardware, this metadata
is passed using the Ethernet control segment of a WQE (a HW descriptor)
header.

The cited commit might nullify this header, hence the metadata is lost,
this caused a significant performance drop during hw offloading
operation.

Fix by restoring the metadata at the Ethernet control segment in case
it was nullified.

Fixes: 37fdffb217 ("net/mlx5: WQ, fixes for fragmented WQ buffers API")
Signed-off-by: Raed Salem <raeds@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/en_tx.c

@@ -387,8 +387,14 @@ netdev_tx_t mlx5e_sq_xmit(struct mlx5e_txqsq *sq, struct sk_buff *skb,
 	num_wqebbs = DIV_ROUND_UP(ds_cnt, MLX5_SEND_WQEBB_NUM_DS);
 	contig_wqebbs_room = mlx5_wq_cyc_get_contig_wqebbs(wq, pi);
 	if (unlikely(contig_wqebbs_room < num_wqebbs)) {
+#ifdef CONFIG_MLX5_EN_IPSEC
+		struct mlx5_wqe_eth_seg cur_eth = wqe->eth;
+#endif
 		mlx5e_fill_sq_frag_edge(sq, wq, pi, contig_wqebbs_room);
 		mlx5e_sq_fetch_wqe(sq, &wqe, &pi);
+#ifdef CONFIG_MLX5_EN_IPSEC
+		wqe->eth = cur_eth;
+#endif
 	}
 
 	/* fill wqe */