ixgbe: fix AF_XDP tx byte count

The tx bytecount is done twice.  When running
'./xdpsock -t -N -i eth3' and 'ip -s link show dev eth3'
The avg packet size is 120 instead of 60. So remove the
extra one.

Signed-off-by: William Tu <u9012063@gmail.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>