net: add GSO UDP L4 and GSO fraglists to the list of software-backed types

Commit e20cf8d3 ("udp: implement GRO for plain UDP sockets.") and
commit 9fd1ff5d

 ("udp: Support UDP fraglist GRO/GSO.") made UDP L4
and fraglisted GRO/GSO fully supported by the software fallback mode.
We can safely add them to NETIF_F_GSO_SOFTWARE to allow logical/virtual
netdevs to forward these types of skbs up to the real drivers.

Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>