tests: Bluetooth: llcp: Add CTE REQ and PHY change collision tests

To avoid violation of BT 5.3 Core Vol 6, Part B section 5.1.10.1
there was added a command pause mechanism that allows to postpone
handling of CTE REQ if there is pending PHY change procedure or
PHY change if there is pending CTE REQ procedure.

The commit adds unit tests for the functionality.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>