net/mlx5e: Add missing sanity checks for max TX WQE size

The commit cited below started using the firmware capability for the
maximum TX WQE size. This commit adds an important check to verify that
the driver doesn't attempt to exceed this capability, and also restores
another check mistakenly removed in the cited commit (a WQE must not
exceed the page size).

Fixes: c27bd171

 ("net/mlx5e: Read max WQEBBs on the SQ from firmware")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>