vlib: refactor checksum offload support

Type: refactor

This patch refactors the offload flags in vlib_buffer_t.
There are two main reasons behind this refactoring.
First, offload flags are insufficient to represent outer
and inner headers offloads. Second, room for these flags
in first cacheline of vlib_buffer_t is also limited.

This patch introduces a generic offload flag in first
cacheline. And detailed offload flags in 2nd cacheline
of the structure for performance optimization.

Change-Id: Icc363a142fb9208ec7113ab5bbfc8230181f6004
Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>
diff --git a/src/vnet/ip/ip4_inlines.h b/src/vnet/ip/ip4_inlines.h
index 3075fbf..00a4712 100644
--- a/src/vnet/ip/ip4_inlines.h
+++ b/src/vnet/ip/ip4_inlines.h
@@ -125,7 +125,7 @@
   if (csum_offload)
     {
       ih->checksum = 0;
-      b->flags |= VNET_BUFFER_F_OFFLOAD_IP_CKSUM;
+      vnet_buffer_offload_flags_set (b, VNET_BUFFER_OFFLOAD_F_IP_CKSUM);
     }
   else
     ih->checksum = ip4_header_checksum (ih);