[NETFILTER]: nf_conntrack_ipv6: fix incorrect classification of IPv6 fragments as ESTABLISHED

The individual fragments of a packet reassembled by conntrack have the
conntrack reference from the reassembled packet attached, but nfctinfo
is not copied. This leaves it initialized to 0, which unfortunately is
the value of IP_CT_ESTABLISHED.

The result is that all IPv6 fragments are tracked as ESTABLISHED,
allowing them to bypass a usual ruleset which accepts ESTABLISHED
packets early.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>