net/mlx5e: Properly set default values when disabling adaptive moderation

Add a call to mlx5e_reset_rx/tx_moderation() when enabling/disabling
adaptive moderation, in order to select the proper default values.

In order to do so, we separate the logic of selecting the moderation values
and setting moderion mode (CQE/EQE based).

Fixes: 0088cbbc ("net/mlx5e: Enable CQE based moderation on TX CQ")
Fixes: 9908aa29

 ("net/mlx5e: CQE based moderation")
Signed-off-by: Tal Gilboa <talgi@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>