[NETFILTER]: Add IPv6 REJECT target

Originally written by Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>,
taken from netfilter patch-o-matic and fixed up to work with current
kernels.

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