ixgbe: remove useless bd_number from adapter struct

Because bd_number is not useful anymore, so remove it from adapter struct, or
if keep it, we have to fix the boards driven counter bug in ixgbe_remove() and
ixgbe_probe() only for trivial debug purpose -- other output is enough.

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>