netfilter: nft_tproxy: restrict support to TCP and UDP transport protocols

stable inclusion
from linux-4.19.198
commit 6b97694d0a76c7b5f5e374dab2a3b1ef54899dc7

--------------------------------

[ Upstream commit 52f0f4e1 ]

Add unfront check for TCP and UDP packets before performing further
processing.

Fixes: 4ed8eb65 ("netfilter: nf_tables: Add native tproxy support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>