mesh: Fix initialization order during node reset

There were several things broken with the initialization order during
node reset:

- The model->flags should not be touched since the writing to
persistent storage happends through delayed work, and the flags
need to be kept until that.

- The unprovision() function should only be called at the very end of
the reset procedure, since it calls model-specific init functions
which may clear things which the earlier reset routines depend on.

nimble/host/mesh/src/access.c

@@ -290,7 +290,6 @@ static void mod_init(struct bt_mesh_model *mod, struct bt_mesh_elem *elem,
 		mod->keys[i] = BT_MESH_KEY_UNUSED;
 	}
 
-	mod->flags = 0;
 	mod->elem_idx = elem - dev_comp->elem;
 	if (vnd) {
 		mod->mod_idx = mod - elem->vnd_models;

nimble/host/mesh/src/cfg_srv.c

@@ -3268,6 +3268,7 @@ int bt_mesh_cfg_srv_init(struct bt_mesh_model *model, bool primary)
 
 	k_delayed_work_init(&cfg->hb_pub.timer, hb_publish);
 	k_delayed_work_add_arg(&cfg->hb_pub.timer, cfg);
+	cfg->hb_pub.net_idx = BT_MESH_KEY_UNUSED;
 	cfg->hb_sub.expiry = 0;
 
 	cfg->model = model;

nimble/host/mesh/src/mesh.c

@@ -79,8 +79,6 @@ void bt_mesh_reset(void)
 		return;
 	}
 
-	bt_mesh_comp_unprovision();
-
 	bt_mesh.iv_index = 0;
 	bt_mesh.seq = 0;
 	bt_mesh.iv_update = 0;
@@ -121,6 +119,8 @@ void bt_mesh_reset(void)
 	bt_mesh_scan_disable();
 	bt_mesh_beacon_disable();
 
+	bt_mesh_comp_unprovision();
+
 	if (IS_ENABLED(CONFIG_BT_MESH_PROV)) {
 		bt_mesh_prov_reset();
 	}