Fix for first RLC tx after handover

lib/src/upper/rlc_am.cc

@@ -112,8 +112,10 @@ void rlc_am::reset()
 
   pthread_mutex_lock(&mutex);
   reordering_timeout.reset();
-  if(tx_sdu)
+  if(tx_sdu) {
-    tx_sdu->reset();
+    pool->deallocate(tx_sdu);
+    tx_sdu = NULL;
+  }
   if(rx_sdu)
     rx_sdu->reset();