[PATCH 2/2] dts: rework run-time MTU adjustment test case

[Nicholas Pratte]

<snip>
>
> The start and stop could be grouped by forwarding sections:
>
>    set_mtu()
>
>    start()
>    assess()
>    assess()
>    stop()
>
>    set_mtu()
>    ...

Alright, I'll fix that real quick!