ixgbevf: Delay tail write for XDP packets

Current XDP implementation hits the tail on every XDP_TX; change the
driver to only hit the tail after packet processing is complete.

Based on
commit 7379f97a ("ixgbe: delay tail write to every 'n' packets")

Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>