Bluetooth: Controller: Revert T_MAFS change done for broadcasting roles

When calculating the offsets between primary advertising
PDU, auxiliary PDU, Periodic Advertising PDU, and BIS PDU,
the values used as anchor points for starting the periodic
interval for auxiliary, periodic and BIG events, should be
ensured to have the minimum auxiliary frame spacing T_MAFS
between the PDUs. EVENT_OVERHEAD_START_US has to be reduced
as this value is used to offset the start of the radio
event on air.

Reverts commit b867f0e8 ("Bluetooth: Controller: Fix
T_MAFS between broadcasting roles").

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