Fixed memory leak due to incorrect freeing of DTLS reassembly bit mask

PR#3608

Reviewed-by: Tim Hudson <tjh@openssl.org>
diff --git a/ssl/d1_lib.c b/ssl/d1_lib.c
index 5f7a358..ab8730c 100644
--- a/ssl/d1_lib.c
+++ b/ssl/d1_lib.c
@@ -187,16 +187,14 @@
     while( (item = pqueue_pop(s->d1->buffered_messages)) != NULL)
         {
         frag = (hm_fragment *)item->data;
-        OPENSSL_free(frag->fragment);
-        OPENSSL_free(frag);
+        dtls1_hm_fragment_free(frag);
         pitem_free(item);
         }
 
     while ( (item = pqueue_pop(s->d1->sent_messages)) != NULL)
         {
         frag = (hm_fragment *)item->data;
-        OPENSSL_free(frag->fragment);
-        OPENSSL_free(frag);
+        dtls1_hm_fragment_free(frag);
         pitem_free(item);
         }