net/mlx5e: Mutually exclude RX-FCS and RX-port-timestamp

Due to current HW arch limitations, RX-FCS (scattering FCS frame field
to software) and RX-port-timestamp (improved timestamp accuracy on the
receive side) can't work together.
RX-port-timestamp is not controlled by the user and it is enabled by
default when supported by the HW/FW.
This patch sets RX-port-timestamp opposite to RX-FCS configuration.

Fixes: 102722fc

 ("net/mlx5e: Add support for RXFCS feature flag")
Signed-off-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>