BLE DTM ll_test does not set correct TXPower

[paulgavrikov]

According to the Bluetooth Core Spec v5 Direct Test Mode shall transmit with maximum txpower. However ll_test sets the txpower to 0dBm, which is not the highest txpower for many device including Nordics nRF52 family.

[cvinayak]

@paulgavrikov if you do have a PR to use the Max Tx Power for nRF5 series SoCs, I will be happy to review the PR.
@carlescufi This will need use re-run tests on the RF tester.

[paulgavrikov]

@cvinayak I don't think I can create a PR for this repo. But you can checkout this commit

[cvinayak]

@paulgavrikov ok. I will prepare a PR and let you know soon.