i40iw: Add missing VLAN priority

Set the VLAN priority which is in the upper 3 bits of the VLAN
tag field in the QP context.

Signed-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>