net/mlx5: LAG, use xa_alloc to manage LAG device indices

net/mlx5: LAG, use xa_alloc to manage LAG device indices

Replace the use of mlx5_get_dev_index() for xarray indexing with
xa_alloc() to dynamically allocate indices. This decouples the LAG
xarray index from the physical device index.

Update mlx5_ldev_add_netdev/remove_mdev to find entries by dev pointer
and replace mlx5_lag_get_dev_index_by_seq(ldev, MLX5_LAG_P1) calls with
mlx5_lag_get_master_idx() where appropriate.

No functional changes intended

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260309093435.1850724-5-tariqt@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>