ixgbevf: remove useless bd_number from struct ixgbevf_adapter

It is useless and buggy, just remove it.

Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>