net/mlx5e: Convert mlx5e_get_max_sq_wqebbs to u8

net/mlx5e: Convert mlx5e_get_max_sq_wqebbs to u8

The return value of mlx5e_get_max_sq_wqebbs is clamped down to
MLX5_SEND_WQE_MAX_WQEBBS = 16, which fits into u8. This commit changes
the return type of this function to u8 for stricter type safety.

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>