ixgbevf: remove redundant workaround

This patch removes a workaround related to header split, which is redundant
because the driver does not support splitting packet headers on Rx.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>