ixgbevf: Remove unused parameter

ixgbevf_update_xcast_mode() is not using the netdev parameter;
removing it since it's unnecessary.

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