The virtchnl interface provides a mechanism for a VF driver to request
head writeback support. This feature is deprecated as of AVF 1.0, but
older versions of a VF driver may still attempt to request the mode.

Since the ice hardware does not support head writeback, we should not
accept Tx queue configuration which attempts to enable it.

Currently, the driver simply assumes that the headwb_enabled bit will
never be set.

If a VF driver does request head writeback, the configuration will
return successfully, even though head writeback is not enabled. This
leaves the VF driver in a non functional state since it is assuming to
be operating in head writeback mode.

Fix the PF driver to reject any attempt to setup headwb_enabled.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>