ipv6: discard overlapping fragment

RFC5722 prohibits reassembling fragments when some data overlaps.

Bug spotted by Zhang Zuotao <zuotao.zhang@6wind.com>.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
int ip6_frag_mem(struct net *net)
{
	return atomic_read(&net->ipv6.frags.mem);
}

int ip6_frag_mem(struct net *net)
{
	return atomic_read(&net->ipv6.frags.mem);
}
