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/examples/vlib/main_stub.c b/src/examples/vlib/main_stub.c
index 3735055..ef6475c 100644
--- a/src/examples/vlib/main_stub.c
+++ b/src/examples/vlib/main_stub.c
@@ -181,7 +181,7 @@
 	  vlib_cli_output (vm, "%U %v: completion #%d type %d data 0x%wx",
 			   format_time_interval, "h:m:s:u",
 			   vlib_time_now (vm), node->name, i, type, data[0]);
-	  _vec_len (data) = 0;
+	  vec_set_len (data, 0);
 	}
 
       vec_free (data);