Bluetooth: controller: conformance test instability

[kruithofa]

Describe the bug
When running conformance tests a few tests are not stable. These tests will pass conformance tests when running stand-alone, but fail when running as part of the complete set of tests to be run.
This behaviour is mainly observed on the Nordic nrf5340 chip

• LL/CON/CEN/BV-121-C
• LL/CON/CEN/BV-57-C
• LL/CON/PER/BV-61-C
• LL/CON/PER/BV-71-C
• LL/CON/PER/BV-73-C
• LL/CON/PER/BV-74-C
• LL/CON/PER/BV-127-C
• LL/DDI/SCN/BV-29-C
• LL/DDI/SCN/BV-48-C

[kruithofa]

On latests runs none of these tests failed; we can re-open if the problems occur again