Revert "devlink: Remove not-executed trap policer notifications"

This reverts commit 22849b5e

 as it
revealed that mlxsw and netdevsim (copy/paste from mlxsw) reregisters
devlink objects during another devlink user triggered command.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>