net/mlx5: LAG, Check correct bucket when modifying LAG

Cited patch introduced buckets in hash mode, but missed to update
the ports/bucket check when modifying LAG.
Fix the check.

Fixes: 352899f3 ("net/mlx5: Lag, use buckets in hash mode")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>