netfilter: nat: fix udp checksum corruption

mainline inclusion
from mainline-v5.2-rc3
commit 6bac76db
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7O0PV
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6bac76db1da3cb162c425d58ae421486f8e43955



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Due to copy&paste error nf_nat_mangle_udp_packet passes IPPROTO_TCP,
resulting in incorrect udp checksum when payload had to be mangled.

Fixes: dac3fe72 ("netfilter: nat: remove csum_recalc hook")
Reported-by: Marc Haber <mh+netdev@zugschlus.de>
Tested-by: Marc Haber <mh+netdev@zugschlus.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>