Bluetooth: controller: Make per. adv. PDUs count related to max CTE num

Amount of memory allocated for advertising PDUs (including
periodic advertising) depends on two factors:
- maximum advertising data length
- maximum number of CTE in a periodic advertising chain.

Maximum advertising data length is divided by maximum size
of a single fragment (number of payload bytes that single
advertising PDU may hold) to get required number of fragments.

Actual number of PDUs allocated for advertising is maximum
of acutal number of advertising payload fragments and maximum
number of CTEs.

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