mesh: Fix IV recovery

mesh: Fix IV recovery

This patch fixes saving IV received in SNB to storage.

Previously after creating new node with IV 0 (or loading node with
IV > 0 but after long inactivity) first received SNB should update IV
(and reset sequence number to 0 if necessary).

The bug would prevent new IV being saved in storage which resulted in
sequence number being set to 0 on first SNB received after every daemon
reset but IV never being updated.

Change-Id: I3767a14a408a33633c374fcdcc08cb6ab68bd9a7
Signed-off-by: Abhay Agarwal <ay.agarwal@samsung.com>