net/mlx5e: Add num bytes metadata to WQE info

For TLS WQEs, metadata info did not include num_bytes. Due to this issue,
tx_tls_dump_bytes counter did not increment.

Modify tx_fill_wi() to fill num bytes. When it is called for non-traffic
WQE, zero is expected.

Fixes: d2ead1f3 ("net/mlx5e: Add kTLS TX HW offload support")
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>