vppinfra: make _vec_len() read-only

Use of _vec_len() to set vector length breaks address sanitizer.
Users should use vec_set_len(), vec_inc_len(), vec_dec_len () instead.

Type: improvement
Change-Id: I441ae948771eb21c23a61f3ff9163bdad74a2cb8
Signed-off-by: Damjan Marion <damarion@cisco.com>

src/plugins/http/http.c

@@ -329,7 +329,7 @@ read_request (http_conn_t *hc)
   if (svm_fifo_is_empty (ts->rx_fifo))
     svm_fifo_unset_event (ts->rx_fifo);
 
-  _vec_len (hc->rx_buf) = cursize + n_read;
+  vec_set_len (hc->rx_buf, cursize + n_read);
   return 0;
 }