Bluetooth: Controller: Fix T_MAFS between 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.

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