NETFILTER: nf_conntrack_tcp: conntrack reopening fix

[NETFILTER]: nf_conntrack_tcp: conntrack reopening fix

[Upstream commits b2155e7f + d0c1fd7a]

TCP connection tracking in netfilter did not handle TCP reopening
properly: active close was taken into account for one side only and
not for any side, which is fixed now. The patch includes more comments
to explain the logic how the different cases are handled.
The bug was discovered by Jeff Chua.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>