net/mlx5e: Accumulate port PTP TX stats with other channels stats

In addition to .get_ethtool_stats, add port PTP TX stats to
.ndo_get_stats64.

Fixes: 145e5637 ("net/mlx5e: Add TX PTP port object support")
Signed-off-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>