Lora: Fix max tx power check

[kivaisan]

Description

In LoRa TX power value 0 means the maximum allowed TX power and values >0
are limiting the allowed TX power to lower.

tx_config was incorrectly checking the power level and causing the maximum
TX power to be always used. Lora gateway can request node to use lower TX
power with LinkAdrReq MAC command.

This fix proposal has been tested with our internal LoRa tests.

Pull request type

[X] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[kivaisan]

@hasnainvirk @AnttiKauppila @kjbracey-arm please review.

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1857
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6740/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : FAILURE

Build number : 1502
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6740/

[mbed-ci]

Test : FAILURE

Build number : 1665
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6740/1665

[kivaisan]

@0xc0170 could you restart the tests? I don't see these fails to relate this PR.

[0xc0170]

/morph test
/morph export-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1508
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6740/

[mbed-ci]

Test : FAILURE

Build number : 1671
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6740/1671

[0xc0170]

/morph test

[0xc0170]

#6740 (comment)

@marcuschangarm Has anything changed in tickers that could cause this failure?

[kjbracey]

That test is supposed to be disabled - see 9f63013. But that has #ifndef MCU_NRF52

But shouldn't that be #ifndef TARGET_MCU_NRF52 (if targets are defined in C? Not sure if they are), or #ifndef NRF52 (which is explicitly set in "macros".).

[kjbracey]

Related issues: #6340 and #6535 - the latter apparently didn't get merged?

[0xc0170]

Yes, there is a fix here now #6756 (as noted previous macro was wrong which was a good thing and did not disable the test but rather to find a fix)

[mbed-ci]

Test : SUCCESS

Build number : 1683
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6740/1683

[hasnainvirk]

@adbridge Why does it need work ? It's all set to go in master.

[0xc0170]

Reviewed, ready for merge

[adbridge]

I marked it as needs work as there are unanswered questions raised by Kevin on this PR.

[kjbracey]

I had no issues - my comments were about the unrelated test failures.

[hasnainvirk]

@cmonr @0xc0170 Could this be merged please ? I have a PR ready to be made which depends on this.