net/mlx4_en: Fix HW timestamp init issue upon system startup

mlx4_en_init_timestamp was called before creation of netdev and port
init, thus used uninitialized values.  Specifically - NIC frequency was
incorrect causing wrong calculations and later wrong HW timestamps.

Fixes: 1ec4864b ('net/mlx4_en: Fixed crash when port type is changed')
Signed-off-by: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: Marina Varshaver <marinav@mellanox.com>
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>