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/ip_frag.c b/src/vnet/ip/ip_frag.c
index 9aa8777..33fbb9b 100644
--- a/src/vnet/ip/ip_frag.c
+++ b/src/vnet/ip/ip_frag.c
@@ -226,7 +226,7 @@
       to_ip4->checksum = ip4_header_checksum (to_ip4);
 
       /* we've just done the IP checksum .. */
-      to_b->flags &= ~VNET_BUFFER_F_OFFLOAD_IP_CKSUM;
+      vnet_buffer_offload_flags_clear (to_b, VNET_BUFFER_OFFLOAD_F_IP_CKSUM);
 
       rem -= len;
       fo += len;