selftests: mlxsw: rtnetlink: Use devlink_reload() API

selftests: mlxsw: rtnetlink: Use devlink_reload() API

The test runs "devlink reload" explicitly. Instead, it is better to use
devlink_reload() which waits for udev events to be processed. Do not sleep
after reload, as devlink_reload() blocks until all the netdevs are renamed.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Link: https://patch.msgid.link/844509e3057b65277a7181a23c95b71ec95e8a56.1727706741.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>