i40e: fix descriptor done flag with odd address

i40e: fix descriptor done flag with odd address

Header buffer address for header split will be filled with the
physical address for DMA, which is actually not needed at all,
as header split hasn't been supported. Hardware requires the
least bit of header address which is 'Descriptor Done' bit when
write back should be set to 0 by driver.
The issue is that if the user wants to reserve an odd number of
bytes between the mbuf header and data buffer, the physical address
to be filled in the descriptor would happen to be odd. That means
the DD bit would be set to non-zero by driver. That will result in
reporting descriptor done wrongly.

Signed-off-by: Helin Zhang <helin.zhang@intel.com>