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>