Bluetooth: Mesh: Prevent CDB reusing address of deleted nodes

According to MshPRFv1.0.1, section 3.10.7, the Provisioner shall only
use reuse addresses of the deleted nodes after IV Index is updated.

This change prevents CDB reusing addresses of the deleted nodes until IV
Index is updated. Due to a high range of the unicast addresses, CDB only
stores the highest deleted address once a node is deleted. This creates
a limitation where allocating a node with the high primary unicast
address and then deleting it will make CDB skip big range of address
until next IV Index update.

Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>