vcl: fix compiling on newer systems

Build fails on ubuntu 17.10...

Change-Id: I98dfffa3f8f5f9bca2ba97a856709714fbeec49c
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/src/vcl/vcom_socket.c b/src/vcl/vcom_socket.c
index afcdc95..de558e7 100644
--- a/src/vcl/vcom_socket.c
+++ b/src/vcl/vcom_socket.c
@@ -30,6 +30,9 @@
 
 #include <vcl/vppcom.h>
 
+#ifndef IOV_MAX
+#define IOV_MAX __IOV_MAX
+#endif
 
 /*
  * VCOM_SOCKET Private definitions and functions.