net/mlx5: Remove not-needed IPsec config

In current code, the CONFIG_MLX5_IPSEC and CONFIG_MLX5_EN_IPSEC are
the same. So remove useless indirection.

Link: https://lore.kernel.org/r/fd14492cbc01a0d51a5bfedde02bcd2154123fde.1649232994.git.leonro@nvidia.com
Reviewed-by: Raed Salem <raeds@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>