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/pg/pg.h b/src/vnet/pg/pg.h
index da2c2b5..da5af25 100644
--- a/src/vnet/pg/pg.h
+++ b/src/vnet/pg/pg.h
@@ -125,9 +125,12 @@
      for max_packet_bytes. */
   u32 buffer_bytes;
 
-  /* Buffer flags to set in each packet e.g. checksum offload flags */
+  /* Buffer flags to set in each packet e.g. l2 valid  flags */
   u32 buffer_flags;
 
+  /* Buffer offload flags to set in each packet e.g. checksum offload flags */
+  u32 buffer_oflags;
+
   /* Last packet length if packet size edit type is increment. */
   u32 last_increment_packet_size;