[PATCH v8 3/3] dts: update tx_offload test from legacy dts to next dts

[Luca Vizzarro]

I've merged the API changes earlier in the day which means that this now
fails because `verify` is a function of `api.test` now.

This also causes a conflict with the variable verify you've been using
across this whole test suite. Looking at it, it seems that this variable
is not actually used at all in a significant way. It's always True,
therefore I'd just remove all the instances of verify, argument of
_check_config as well, and use the verify=True default as-is.

Finally, I've realised that the commit subject is incompatible. This
should just be something along the lines of:

  dts: add rx tx offload test suite