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>
diff --git a/src/vlibmemory/memory_shared.c b/src/vlibmemory/memory_shared.c
index 1716f27..5244b27 100644
--- a/src/vlibmemory/memory_shared.c
+++ b/src/vlibmemory/memory_shared.c
@@ -545,8 +545,8 @@
   if (strstr (region_name, vpe_api_region_suffix))
     {
       u8 *root_path = format (0, "%s", region_name);
-      _vec_len (root_path) = (vec_len (root_path) -
-			      strlen (vpe_api_region_suffix));
+      vec_set_len (root_path,
+		   vec_len (root_path) - strlen (vpe_api_region_suffix));
       vec_terminate_c_string (root_path);
       a->root_path = (const char *) root_path;
       am->root_path = (const char *) root_path;