Etherlink: tx queue uses keep alive

Checklist

- [ ] Provide automatic testing.

• Add an item in the changelog

What, why and how

meta-issue for the stacked MR: #7785

keep_alive was hardcoded on the Tx_queue. This simply replace that by using the value in the config.

Manually testing the MR

run with and without the keep_alive in the config and make sure it behaves as expected.