Bluetooth: Controller: Fix Adv PDU RAM usage for direction finding

Fix Advertising PDU size calculation when direction finding
feature is enabled and PDU fragment count includes the
maximum CTE PDU chained. Fix removes redundant PDU count
included for Extended Advertising. Only Periodic advertising
PDUs chain CTE requires number of additional PDUs.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>