zebra: Ensure that changes to dg_update_list are protected by mutex

The dg_update_list access is controlled by the dg_mutex in all
other locations.  Let's just add a mutex usage around the initialization
of the dg_update_list even if it's part of the startup, just to keep
things consistent.

Signed-off-by: Donald Sharp <[email protected]>

zebra/zebra_dplane.c

@@ -7698,7 +7698,9 @@ static void zebra_dplane_init_internal(void)
 
 	dplane_prov_list_init(&zdplane_info.dg_providers);
 
-	dplane_ctx_list_init(&zdplane_info.dg_update_list);
+	frr_with_mutex(&zdplane_info.dg_mutex)
+		dplane_ctx_list_init(&zdplane_info.dg_update_list);
+
 	zns_info_list_init(&zdplane_info.dg_zns_list);
 
 	zdplane_info.dg_updates_per_cycle = DPLANE_DEFAULT_NEW_WORK;