Introduce l{2,3,4}_hdr_offset fields in the buffer metadata

To save space in the first cacheline following is changed:

- total_length_not_including_first_buffer moved to the 2nd cacheline.
This field is used only when VLIB_BUFFER_TOTAL_LENGTH_VALID and
VLIB_BUFFER_NEXT_PRESENT are both set.

- free_list_index is now stored in 4bits inside flags, which
allows up to 16 free lists. In case we need more we can store index
in the 2nd cachelin

Change-Id: Ic8521350819391af470d31d3fa1013e67ecb7681
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/src/vnet/dhcp/dhcp6_proxy_node.c b/src/vnet/dhcp/dhcp6_proxy_node.c
index 885313a..e109cc4 100644
--- a/src/vnet/dhcp/dhcp6_proxy_node.c
+++ b/src/vnet/dhcp/dhcp6_proxy_node.c
@@ -306,7 +306,7 @@
           copy_ip6_address(&r1->link_addr, ia0);
 
         link_address_set:
-          fl = vlib_buffer_get_free_list (vm, b0->free_list_index);
+          fl = vlib_buffer_get_free_list (vm, vlib_buffer_get_free_list_index (b0));
 
           if ((b0->current_length+sizeof(*id1)+sizeof(*vss1)+sizeof(*cmac))
               > fl->n_data_bytes)