nr rlc: fix a bug

The count was wrong.

openair2/LAYER2/nr_rlc/nr_rlc_entity_am.c

@@ -1284,7 +1284,7 @@ static int missing_size(nr_rlc_entity_am_t *entity, missing_data_t *m,
   missing_data_t m_nack;
 
   /* be careful to limit a range to 255 SNs, that is: cut if needed */
-  sn_count = m->sn_end - m->sn_start;
+  sn_count = m->sn_end - m->sn_start + 1;
   if (sn_count < 0)
     sn_count += entity->sn_modulus;