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: dac3fe72596f9 ("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>