net/mlx5: Restore mistakenly dropped parts in register devlink flow

Code parts from cited commit were mistakenly dropped while rebasing
before submission. Add them here.

Fixes: c6e77aa9

 ("net/mlx5: Register devlink first under devlink lock")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/r/20240411115444.374475-4-tariqt@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>