Bluetooth: Controller: Fix AUX_ADV_IND AUX_SYNC_IND radio utilization

Fix AUX_ADV_IND AUX_SYNC_IND radio utilization by having a
configurable offset.

Define an offset between AUX_ADV_IND and AUX_SYNC_IND when
using Advertising Interval for the Extended Advertising and
Periodic Advertising that are same or multiple of each
other, respectively.

Note, to get advertising intervals that are same or
multiple, the Periodic Advertising Interval shall be 10
millisecond more than the Extended Advertising Interval;
this is because the AUX_ADV_IND PDUs are scheduled as
periodic events of Extended Advertising Interval plus 10
milliseconds (Advertising Random Delay) as the periodic
interval.

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