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/vnet/ip/reass/ip6_sv_reass.c b/src/vnet/ip/reass/ip6_sv_reass.c
index 23ae678..e1493c9 100644
--- a/src/vnet/ip/reass/ip6_sv_reass.c
+++ b/src/vnet/ip/reass/ip6_sv_reass.c
@@ -734,7 +734,8 @@
 						 to_next, n_left_to_next, bi0,
 						 next0);
 	      }
-	      _vec_len (reass->cached_buffers) = 0;	// buffers are owned by frame now
+	      vec_set_len (reass->cached_buffers,
+			   0); // buffers are owned by frame now
 	    }
 	  goto next_packet;
 
@@ -1050,7 +1051,7 @@
       vec_free (pool_indexes_to_free);
       if (event_data)
 	{
-	  _vec_len (event_data) = 0;
+	  vec_set_len (event_data, 0);
 	}
     }