tcp: fix mark propagation with fwmark_reflect enabled
Otherwise, RST packets generated by the TCP stack for non-existing
sockets always have mark 0.
The mark from the original packet is assigned to the netns_ipv4/6
socket used to send the response so that it can get copied into the
response skb when the socket sends it.
Fixes: e110861f8609 ("net: add a sysctl to reflect the fwmark on replies") Cc: Lorenzo Colitti <lorenzo@google.com> Signed-off-by: Pau Espin Pedrol <pau.espin@tessares.net> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>