Bluetooth: controller: split: Fix advertising for multiple peripherals

When multiple simultaneous peripheral connections are
supported, restarting connectable advertising by host on
peripheral connection establishment failed in controller.
This prevented establishing new connections while first
connection was active.

The failure was caused by a bug in the way controller was
using quota for Rx PDU buffers. As the quota count was
release before the connection complete event rx PDU buffer
being released, the Rx PDUs needed to reserve for
connection complete event for new connectable advertising
was not available. This caused the connectable advertising
enable to fail.

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