netfilter: use ipv4 iptables rules to block IPv4-mapped IPv6 addresses

If ipv6 socket has an IPv4-mapped address, it is used to handle ipv4
connection, so we have to use ipv4 iptables rules to block this
connection.

Reported-by: Mr Jenkins
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>