Summary of changes
Sometimes lorawan test was not 100% OK when it is executed many times.
Impact of changes
Migration actions required
Pull request type
[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)  Feature update (New feature / Functionality change / New API)  Major update (Breaking change E.g. Return code change / API behaviour change)
 No Tests required for this change (E.g docs only update) [x] Covered by existing mbed-os tests (Greentea or Unittest)  Tests / results supplied as part of this PR