net: introduce a netdev feature for UDP GRO forwarding

[ Upstream commit 6f1c0ea1 ]

Introduce a new netdev feature, NETIF_F_GRO_UDP_FWD, to allow user
to turn UDP GRO on and off for forwarding.
Defaults to off to not change current datapath.

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 9cfb5e7f ("net: hsr: fix hsr_init_sk() vs network/transport headers.")
Signed-off-by: Sasha Levin <sashal@kernel.org>