Incorrect xt_iprange boundary check for IPv6

[Thomas Jacob <jacob@internet24.de>]

Developed for and tested on 2.6.27.57, but applies and compiles
in current mainline as well (haven't tested it there though).

See the following script for a demonstration of the problem:

#!/bin/sh
PREFIX=fc42:4242
LEFTOUT=$PREFIX:0:ffff:ffff:ffff:ffff:ffff
FROM=$PREFIX:1::0
MIDDLE=$PREFIX:1::8000:0:0:0
TILL=$PREFIX:1::ffff:ffff:ffff:ffff
RIGHTOUT=$PREFIX:2::0
SUBNET=$PREFIX:1::/64
SOURCE=fc23:2323::1
CHAIN=iprange_bug

ip6tables -S OUTPUT | fgrep -q -- '-A OUTPUT -j '"$CHAIN" \
	&& ip6tables -D OUTPUT -j $CHAIN

ip6tables -F $CHAIN 2>/dev/null
ip6tables -X $CHAIN 2>/dev/null
ip6tables -N $CHAIN

ip6tables -A $CHAIN -p icmpv6 --icmpv6-type echo-request -s $SOURCE -m iprange --dst-range $FROM-$TILL
ip6tables -A $CHAIN -p icmpv6 --icmpv6-type echo-request -s $SOURCE -d $SUBNET -j DROP

ip6tables -I OUTPUT 1 -j $CHAIN

ip addr replace $SOURCE/128 dev lo
ip addr replace $LEFTOUT/128 dev lo
ip addr replace $FROM/128 dev lo
ip addr replace $MIDDLE/128 dev lo
ip addr replace $TILL/128 dev lo
ip addr replace $RIGHTOUT/128 dev lo

for IP in $LEFTOUT $FROM $MIDDLE $TILL $RIGHTOUT
do
	ping6 -c 1 -W 1 -q -I $SOURCE $IP | grep ^PING
done

echo
ip6tables -vnL $CHAIN

ip addr del $RIGHTOUT/128 dev lo
ip addr del $TILL/128 dev lo
ip addr del $MIDDLE/128 dev lo
ip addr del $FROM/128 dev lo
ip addr del $LEFTOUT/128 dev lo
ip addr del $SOURCE/128 dev lo

ip6tables -D OUTPUT -j $CHAIN
ip6tables -F $CHAIN
ip6tables -X $CHAIN