[Backport-v2.2-branch] Bluetooth: controller: legacy: DLE timing

Fixes #23482.

There is a bug in calculation of time for the DLE procedure:
the preamble size is incorrect for the 2M phy

This is for the legacy code, see PR #23570 for the split controller

Signed-off-by: Andries Kruithof <Andries.Kruithof@nordicsemi.no>