ixgbevf: Add netdev to ring structure

This change adds the netdev to the ring structure.  This allows for a
quicker transition from ring to netdev without having to go from ring to
adapter to netdev.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>