net/mlx5e: Fix calculations related to max MPWQE size

Before commit 76c31e5f ("net/mlx5e: Use FW limitation for max MPW
WQEBBs"), the maximum size of MPWQE in WQEBBs was hardcoded as a driver
constant. That commit started using the firmware capability that can
further limit the size, however, it unintentionally changed a few
things:

1. The calculation of MLX5E_MAX_KLM_PER_WQE used the size in DS, which
was replaced by the size in WQEBBs, making the resulting value 4 times
smaller.

2. MLX5E_TX_MPW_MAX_WQEBBS used to be aligned to the cache line size
(either 64 or 128 bytes, i.e. 1 or 2 WQEBBs), but it's no longer the
case if the firmware capability is smaller than the driver maximum.

Fix both issues by using the correct units for MLX5E_MAX_KLM_PER_WQE and
by aligning mlx5e_get_sw_max_sq_mpw_wqebbs after taking the minimum.

Besides fixing the arithmetics in calculation of MLX5E_MAX_KLM_PER_WQE,
also use appropriate constants: `size of BSF * num of DS per WQEBB *
number of WQEBBs` (the calculation before the blamed commit) doesn't
make much sense to calculate the WQE size in bytes, so just use `size of
WQEBB * number of WQEBBs`.

While at it, replace the types that hold the number of WQEBBs by u8.
These values don't exceed 16, and it allows to fill holes in two
structs.

Fixes: 76c31e5f ("net/mlx5e: Use FW limitation for max MPW WQEBBs")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>