i40e/i40evf: set headwb Tx context flags and use them

i40e/i40evf: set headwb Tx context flags and use them

Set appropriate fields in Tx queue configuration virtchnl message
to pf to enable headwb and setup headwb addr.
Then use that info from the VF to set headwb and headwb_addr instead of
always enabling them.

Change-ID: I7d393d1b2b07f0f3355b3a4f7c2d3c6ee3b0d622
Signed-off-by: Ashish Shah <ashish.n.shah@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>