white-ice: Remove warning message

It is possible to find login attempts from blocked clients if the
attempts come in faster than we block clients. Thus we should not
warn about this.
white-ice: Bug fix

Both stdout and stderr should be direct to /dev/null.
white-ice: Handle login attempts with invalid user
white-ice: Bug fix for iptables_input_rulenum()

This commit fixes problems in iptables_input_rulenum(), in
particular the incorrect handling of the first line in the
iptables -nvL INPUT output.
white-ice: Do not store the rule number

The rule numbers are changing all the time when blocking new
clients so it really makes no sense to store it as part of
the client. We rather should retrieve it just-in-time in the
unblock() function. Since we generally do not support unblocking
of clients this has not been an issue before.