net: Add a netdev software feature set that defaults to off.

The previous patch added the NETIF_F_GRO_FRAGLIST feature.
This is a software feature that should default to off.
Current software features default to on, so add a new
feature set that defaults to off.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>