igb: replace the VF clear_to_send with a flags value

In order to support future features it is easiest to replace the
clear_to_send boolean with a flag value.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>