Bluetooth: controller: ULL: Make API for per adv sync PDU change global

Some functions, provided to handle changing content of periodic
advertising PDUs, were defined as static.
Code responsible for handling direction finding updates periodic
advertising PDUs also. For that purposes, those functions were mede
globally accessible.

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