net/mlx5e: Remove unused fields from datapath structs

No need to keep max_sq_wqebbs in mlx5e_txqsq and mlx5e_xdpsq, as it's
only used when allocating the queues. Removing an extra field reduces
the struct size.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>