i40e: partition the ring_cookie to get VF index

Do not use the user-def field for determining the VF target. Instead,
similar to ixgbe, partition the ring_cookie value into 8bits of VF
index, along with 32bits of queue number. This is better than using the
user-def field, because it leaves the field open for extension in
a future patch which will enable flexible data. Also, this matches with
convention used by ixgbe and other drivers.

Change-Id: Ie36745186d817216b12f0313b99ec95cb8a9130c
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>