net/mlx5e: Add PTP-RX statistics

Like PTP-TX, once the PTP-RX is opened, corresponding statistics appear.
Add indication that PTP-RX was ever opened: rx_ptp_opened. If any of the
PTP RX or TX were opened, display the PTP channel's statistics.

Signed-off-by: Aya Levin <ayal@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>