Bluetooth: controller: Initialize PDUs in set #0 on reset

Set #0 is used for legacy advertising when legacy HCI commands are used
and in such case it's possible to enable advertising without any prior
configuration. This means we should better always have PDUs in set #0
initialized with default empty data.

Signed-off-by: Andrzej Kaczmarek <andrzej.kaczmarek@codecoup.pl>