netfilter: xt_recent: inform user when hitcount is too large

It is one of these things that iptables cannot catch and which can
cause "Invalid argument" to be printed. Without a hint in dmesg, it is
not going to be helpful.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>