nr rlc tm: bugfix: reset t_current when clearing entity

maybe not super important, but let's harmonize with um/am

openair2/LAYER2/nr_rlc/nr_rlc_entity_tm.c

@@ -188,6 +188,8 @@ void nr_rlc_entity_tm_discard_sdu(nr_rlc_entity_t *_entity, int sdu_id)
 
 static void clear_entity(nr_rlc_entity_tm_t *entity)
 {
+  entity->t_current = 0;
+
   entity->t_log_buffer_full = 0;
   entity->sdu_rejected      = 0;