net/mlx5e: Remove the false indication of software timestamping support

[ Upstream commit 47654204 ]

mlx5 driver falsely advertises support of software timestamping.
Fix it by removing the false indication.

Fixes: ef9814de ("net/mlx5e: Add HW timestamping (TS) support")
Signed-off-by: Alaa Hleihel <alaa@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>