test::radio::run() does not behave similar to nrf52::run()

[TorstenRobitzki]

The described behavior of run() in schedule_radio is not very clear. The nrf52 implementation works well with link_layer, but link_layer makes assumptions on the behavior of run() that holds true, when it comes to the nrf52 implementation, but not when it comes to the test implementation.

As link_layer::run() expects that radio::run() will return after every connection event behavior differs, when it comes to sending of pending l2cap PDUs (Notification / indications).

This should be clarified and unified!