Bluetooth: Mesh: Change IV Update duration requirement for new nodes

Mesh Profile specification errata 11627

Section 3.10.5:
When a node is added to a network, the node is given an IV Index.
If the node is added to a network when the network is in Normal
operation, then it shall operate in Normal operation for at least
96 hours. If a node is added to a network while the network is in
the IV Update in Progress state, then the node shall be given the
new IV Index value and operate in IV Update in Progress operation
without the restriction of being in this state for at least 96 hours.

Signed-off-by: Michał Narajowski <michal.narajowski@codecoup.pl>