Make ip csum configurable in vlib buffer functions

Also fixes csum computation for lisp control plane 4o6 encapsulated control
messages.

Change-Id: I991e0b5c0d16dc51e0b5bdc79e1d752270b34765
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vnet/lisp-cp/lisp_msg_serdes.c b/src/vnet/lisp-cp/lisp_msg_serdes.c
index 6c0a721..aee4f25 100644
--- a/src/vnet/lisp-cp/lisp_msg_serdes.c
+++ b/src/vnet/lisp-cp/lisp_msg_serdes.c
@@ -229,7 +229,7 @@
     }
 
   /* Push inner ip and udp */
-  pkt_push_udp_and_ip (vm, b, lp, rp, src_ip, dst_ip);
+  pkt_push_udp_and_ip (vm, b, lp, rp, src_ip, dst_ip, 0);
 
   /* Push lisp ecm hdr */
   h = pkt_push_ecm_hdr (b);