avf: fix l2_len for csum offload

Use vlib_buffer_t::current_data instead of
vnet_buffer_opaque_t::l2_hdr_offset to compute l2_len for checksum
offload (l2_hdr_offset might be invalid if packet originates from an L3
interface)

Change-Id: I2031ea6fd6a7af4b6e186751e119ebd6161641b5
Type: fix
Signed-off-by: Mohammed Hawari <mohammed@hawari.fr>
diff --git a/src/plugins/avf/output.c b/src/plugins/avf/output.c
index 55a01c7..952d151 100644
--- a/src/plugins/avf/output.c
+++ b/src/plugins/avf/output.c
@@ -67,7 +67,7 @@
   u32 is_ip6 = b->flags & VNET_BUFFER_F_IS_IP6;
   ASSERT (!is_tcp || !is_udp);
   ASSERT (is_ip4 || is_ip6);
-  i16 l2_hdr_offset = vnet_buffer (b)->l2_hdr_offset;
+  i16 l2_hdr_offset = b->current_data;
   i16 l3_hdr_offset = vnet_buffer (b)->l3_hdr_offset;
   i16 l4_hdr_offset = vnet_buffer (b)->l4_hdr_offset;
   u16 l2_len = l3_hdr_offset - l2_hdr_offset;
@@ -156,9 +156,8 @@
   /* Acquire a reference on the placeholder buffer */
   ctx_ph->ref_count++;
 
-  u16 l234hdr_sz =
-    vnet_buffer (b)->l4_hdr_offset -
-    vnet_buffer (b)->l2_hdr_offset + vnet_buffer2 (b)->gso_l4_hdr_sz;
+  u16 l234hdr_sz = vnet_buffer (b)->l4_hdr_offset - b->current_data +
+		   vnet_buffer2 (b)->gso_l4_hdr_sz;
   u16 tlen = vlib_buffer_length_in_chain (vm, b) - l234hdr_sz;
   d[0].qword[0] = 0;
   d[0].qword[1] = AVF_TXD_DTYP_CTX | AVF_TXD_CTX_CMD_TSO