Decide on ordering of Tx/Rx pairs in APIs

[MabezDev]

We should decide on an order, and add it to the API guidelines, then check that all APIs that return or consume a tx/rx pair use that order.

[bugadani]

Well, obviously tx, rx is the only right way to do it :)

Btw we might want to think about this a bit more generally, there are some inconsistent things in the HAL, like:

(timer, clocks, vs clocks, timer)

[AnthonyGrondin]

embassy-net and smoltcp both seem to be using rx, tx.

[MabezDev]

In our internal meeting we decided to try and be consistent with the ecosystem, we will use rx, tx.

[SergioGasquez]

Well, obviously tx, rx is the only right way to do it :)

Btw we might want to think about this a bit more generally, there are some inconsistent things in the HAL, like:

(timer, clocks, vs clocks, timer)

I guess after #1999 clocks/timer is no longer an issue