[NETFILTER]: ipt_recent: last_pkts is an array of "unsigned long" not "u_int32_t"

This fixes various crashes on 64-bit when using this module.

Based upon a patch by Juergen Kreileder <jk@blackdown.de>.

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