bluetooth: mesh: Fix IVU duration counter update

When device is first provisioned with IV Update
flag is set to 0, it should wait for minimum of
96 hours before going into IV Update In Progress
state. Such limit does not apply, if device is
provisioned with IV Update flag is set to 1.

Signed-off-by: Omkar Kulkarni <omkar.kulkarni@nordicsemi.no>